1. Mark at beginning to which Fallout version it applies
2. Its about your opinion only and
3. .. its limited to your opinion only. Do not engage in +/- wars, Your message is heard if you posted it. Posting is sufficient.
4. This is done to give lesson/ideas to future developers, not to dig fallout into the ground
5. Preferably keep every idea as compact as possible, but its not obligatory
....
7. See (3) again.
8. Share your thoughts freely.

Go!

F1-2:
- NPC+player sprites are badly done: 1) when friend first introduced me to fallout (it was fallout 1) I was turned down mostly by how people look in Fallout. 2) after I got hooked to Fallout, many many years later my ... children claimed the same to me when they saw the game first time. 3) reversing the sprites back to 3d, may show the idea. 4) additional effect may be attributed to absence of vertical move direction and hence weird movement in F. 5) fairly good comparison of better sprite quality is imho - Jagged Alliance 2. 6) sprite style in F is iconic (consistent), I don't question this. Some titles do push "iconic" quality to extent that style wins over quality, for example Space Quest 6.
- you level up by killing mostly
- looting is limited to player
- player has god-like overview of local map, where NPCs have little vision of detecting player
- NPCs are triggered on whole map and are instantly aware of what is actually happening
- way excessive sex* stuff
- way too much political connection with real countries
- way too much americanism, involvement of other countries is almost non-existent
- text messages are good, but very scarce
- raiders are useless bullet sponges having little agenda
- monster size and weapon specifics do not affect chance to hit
- monster difficulty is predominantly expressed in its hit damage * action points, instead of interaction with environment or its special abilities
- actually pretty limited dialog options
- unrealistic tribal-like society rebuild
- too much ammunition, too little factories
- force gates in NCR (F2), but nobody can make electric motor and cars
- low game replayability
- outdoor problem (Tauto is author, agreeing): on encounter, you will always find yourself in the middle of action if your outdoor skill is low; and that skill is always low at beginning, so you will always find yourself either dying, reloading or A-key-tactically-cheating out of the area. Better way would probably be to throw a chance, then if succeeded throw roll as of distance to action, based on the skill with some corrections also taking perception of enemy.
- many locations are quest-locked, even though you would bump into them when traveling in reality
- bad weapon range causes AG stat to become life-saver, but it shouldn't be
- weapon skills should've been structured as a tree-like specialization instead of separate skills
- first-aid and doctor skills are duplicates
- science finds rare application and conflicts with doctor skill sometimes
- steal skill and trap skill are useless
- skill point progression is unrealistic - going 0->100 skill is equal to going 0->33 in three skills
- most of traits are useless, because they give back no/very little benefit
- most perks are useless or unbalanced in benefits between each other
- iconic Dogmeat is very weak, has no armor options and is a big nuisance
- dog followers can carry almost as much weight as human one
- "LUCK" stat, why is it there at all? Why isn't it a derivative stat, similar to Sequence
- karma is often subjectively applied: F2 new reno 3 gangs are evil, 1 gang is good, even though its members and crimelord trigger against you as easily as other 3
- karma balance is unrealistic: stabbing someone to death, but helping another person next day results in neutral karma! Good karma is very cheap, evil is rare and evil actions have low weight
- (derivation of above) its hard to be evil. Lots of monsters rare really evil rewards
- game BOSSes showcase themselves very clearly and their agenda is very paved out (binary, has little facets)
- you become more skilled by reading books, but not through practice. That leads to "becoming genius scientist through slaying geckos" logic.
- ....
more?

All Fallouts:
- everything about ghoul nature - I can't understand how simple radiation can produce beings that are capable to survive 200+ years (technically, to decompose 200+ years while attracting flies), with no food and drink,with random nature of going feral
- then again, main character can't become ghoul and always dies of radiation poisoning.
- stimpacks are source of unlimited hp points with little effects that are nowhere produced and everywhere abundant
- ... and npcs use them very scarcely and don't pile them up
- all medications/drugs have no best-before

Fallout 3 and 4.

NPC's look stupid.
They are not isometric and turn based and instead plays too much like a uninspired FPS game.
Quest and Storyline are utter garbage.
The games are very buggy.
They play like trash and the majority of perks are boring and useless.
Worst dialgue interactions and choices ever.
Morality don't matter.
Factions are boring, doesn't feel unique enough and are full of idiot npc's.
Power armor is ruined in Fallout 4 and made it into instant gratification reward without having a to earn anything.
UI and HUD looks and feels amateurish.
James and Shaun should never have been involved in main story.
AI is atrocious like nothing else.
Nuka World, Mothership Zeta and Operation Anchorage is one of the worst DLC's you can pay for.
Settlement Building is crap and should never have made it into the game and certainly not part of paid DLC.
They are made by crapthesda.
Graphics looks washed out and textures are disgusting.
Hardcore mode feels like a afterthought.
Most of the companions are trash and annoying.
Can't avoid Preston Garvey and his gang of morons.
Companions likes and dislikes are poorly implemented and hinders gameplay.
Travis both versions is annoying and ruins the game by himself.
None of the games have a single redeeming thing about them.
Stats are almost useless and don't have the importance they should have.
Legendary enemies including robots mutate when taking fatal damage first time and it's fucking hilarious, SO BAD.
Legendary weapons and armor are uninteresting and does not feel exciting which in turn makes looting pointless and feels like a borderlands clone which is a shame because i consider all Borderlands games to be beyond horrible.

F2:
-missed opportunity with husband/wife companion (just another companion, rather weak in fight, lack of some sort side-quest(series) which would develop bond with husband/wife)
-quantity over quality in terms of locations/NPCs/etc (despite the fact that F1 was a bit humble in some aspects, it had more memorable/interesting characters & locations)
-can't join "main bad guys"
-long and annoying "innitial phase" of game when you have hard time to collect more caps (and buy/obtain some decent firearms) - it's rathey annoying than challenging

F1
- "human companions" becaming rather useless in later parts of the game, during fight with more difficult enemies (e.g. supermutants)
- you can in theory join to "main bad guys", but in practice it's incredibly easy and game threatens this as game over with different end animation

F1-F2
- small firearms are only "transition" on the road to heavy weapons/energetic weapons, you basically must develop this skill, but later it becomes useless (not counting single exception of Gauss Rifle)
- companious are useful (or not) basing almost only on their weapon preferences, some single exceptions who have some other abilities (like Myron in F2) are not especially worthy your time (and "slot" in squad capacity)
- humble amount and sometimes silly looking animations (single example - compare shooting animation in F1-F2 and in Fallout Tactics, where you character can shoot with holding weapon near cheek (aiming) or shooting with "hip shot") Plus this silly looking "use" animation (used for many situations).

Fallout New Vegas:

- Bugs
- More bugs
- Even more bugs (it's Obsidian, I shouldn't be surprised)

- Lack of memorable characters
- Boring sandy environment
- Lacks the personality and sense of humour that was in Fallout 3
- Lost the aesthetic that made Fallout 3 memorable

Fallout in general:

- The overall fan base. A group of small minded people who are so ignorant that it hurts.

Like these? (Warning: Site may play audio if no adblock)
http://fallout.wikia.com/wiki/Cazador

At the end of that article, probably.

Fallout 2

That game was pretty much ruined for me by its tasteless "humour", way too many pop culture references, and some really disgusting sex stuff (you lose in armwrestling against that mutant? You're now his sex toy for the night and get ball-gagged!).
Also failed totally at creating a believable post-apocalyptic world, something like that casino city with its crime families and porn studios was just ridiculous. Killed all immersion for me.
The main story was really bad, a cheap copy of the plot of the first game, but a lot worse. Really bad pacing. For most of the game, the main baddies hardly play any role, they only get more prominent right at the end of the game.
The combat was also tedious. Unlike in Fallout 1 there even was a long stretch at the game's beginning where you don't have firearms and have to use melee. Fighting those geckos with your fists or a spear got old pretty fast.
I also played an unpatched version, so I suffered from many of the game's aggravating bugs, like the disappearing car trunk.
Fallout 2 is really a massively overrated game imo, and pretty flawed. The first game is also overrated, but much better and more fun imo.

F3-FNV:
- pipboy, looks like a 40 kg brick, that nobody would ever use
- ... and nearly nobody uses pipboys, except player and few npcs
- ... ... so then why is it essential
- VATS, in 3d world aimed-shot-screen would be better replaced with bullet time, but corrected in F4
- lots of unused garbage, that is even reused in various quests, making it really difficult to distinguish between what is garbage and what is useful
- billboards, paint of which has survived nuclear blasts and following 100+ years of sun exposure
- cannibalism. F1-2 had perks which could only be gained outside of leveling, by events or actions, perfect example would be "addiction perks". this would be perfect target, but you need to level up to become cannibal and you can do it instantly
- some brands are actively "forced into face" (nuka cola, sunset sarsaparilla), compared to f1-2 where no item had such a focused attention, and their backstory and importance were to be discovered by reading, talking and exploring instead. Also compare to other items like "abraxo cleaner",
- some of items on npc behave differently on player, for example: hazmat suit
- radiation suit, having isolation fabric and closed breathing system - does not protect against poison
- a lot of old guns were abolished and replaced with new guns causing parallel universe effect rather than expansion.

F3:
- many quests and quest timelines are left unconnected, isolated from each other
- most of quests are very shallow / little effort
- the idea of hand-made weapons is nice, but implementation of some of them was weird

F:NV:
- hardcore is really not hardcore
- way to little radiation, radiation is way to easy to manage
- can't skip the new "GOAT/Temple of trials". RPG start mod fixes it
- karma system is back and again a plain pain. For example, stealing weapon from serial killer is considered a crime.

More?

The idea is not to give reaction if you disagree, like brain storming.
If same idea surfaces in many posts, then it may be applicable. More - then more probable that its true.
If you disagree, it does not cancel that original poster opinion - so arguing is virtually useless.
Feel free to open dedicated topic to discuss that specific point.

Also, (3) because of this.

Also "good/bad" does not intersect with "iconic". Could be said that sprite looks in F1-2 are iconic to the series, which does not cancel if someone finds them bad looking.

As to why I personally find them bad, I will expand the section. You are welcome to contribute what would YOU do differently.

Sure,there are bugs and crashes and that's where saving often helps.F3 and FNV.My only gripe is no matter how many times you start a game and sneak around,you can always get the jump on the baddies as they have a set movement pattern.Now if they were unpredictable in their patrol/movement and a lot sneakier that would make it a little tougher.

I see it the same way! I also updated my own post. Thanks!

FO3 + NV:

- Way too much loot just lying around in cities. Downright immersion-breaking. That stuff would have been picked clean within a year.

- Difficulty is too easy. And no, turning enemies into bullet-sponges that hit like trucks isn't how you fix it. Clearly balance took a back-seat to world-building. Imagine how great FNV would be if it actually had a sense of danger, if you had to play tactically, tailor your approach to each fight and ration limited resources. I don't normally do a first playthrough with mods but if I could go back and do that with FNV, I would.

- Inventory management. Gamers learn to loot everything that isn't nailed down, yet here it slows the game down tremendously. You want a companion just as a pack mule, and that messes with the difficulty even more.

All of them:

- Radiation. Why have a game mechanic that only shows up like twice in an entire playthrough? Makes about as much sense as combat in a point & click. It's clearly there just as a world-building device, not for gameplay purposes.

I haven't played the games myself, but here are some of mine based off what I've read:

Classic Fallout:
* HP gains from Endurance are not retroactive. (In other words, characters who develop Endurance later end up with less HP in the long run than those that get that Endurance early.)
* Perks like Lifegiver have similar non-retroactive effects. (Apparently, Fallout Tactics has a perk that affects the rate at which you get perks, creating similar issues.)

Modern Fallout:
* Is not in the same genre as classic Fallout.

Entire series:
* No spells. Remember the days when RPGs would be advertised with the number of spells in them (as well as monsters, items, and dungeon levels)? Well, Fallout fails on this front. (To be fair, this probably isn't objectively a fault, but more the fact that I prefer fantasy settings in games.)
* Skills don't increase from usage. (The increase of skills from usage is the one mechanic that made me choose to play Wasteland, but it's not found here.) Instead, there's a skill point system, with all the issues it has.

(Also, why is this post here and not on the appropriate sub-forum?)