Final Fantasy 9 - Split my party wrong about halfway through, didn't have a save from before I split them up.

Thief 3: Deadly Shadows - I keep trying to play this game, it never works out.

Ninja Gaiden 2 - Forever stuck on the last boss.

Snatcher - Stuck on the last shootout.

Black and White - Didn't feel it worth grinding the last Island.

Max Payne 2 - It never compels me to finish it.

Back to the Future - I hate adventure games, this sealed it.

Shadow of the Colosus - Never interests me enough.

Killer7 - I totally hate this game, yet I don't want to get rid of it.

Pirates of the Carribean - This is not getting any better with age.

Ultima IV
Failed on the very last question.

Wasteland
I had fought a gazillion random encounter against the amassed robot hordes of the known Universe in Vegas, when the game got corrupted. Wild whores could not make me play through Vegas again.

Star Command
Bugged out after blowing up the bugs' main computer.

Wizardry V
Game bugge(re)d out on me at the very end.

Anvil of Dawn
Kept crashing near the end

Might&Magic VI
Playing turn based against the robots in the Control Center near the end is apparantly not a good idea.

Star Trek: The Next Generation – A Final Unity - Got very close to finishing, but decided to hold off so as to "prolong" the game. Unfortunately, I misplaced the CD. 20 years later, I suddenly found it when I was looking for something else, but haven't had a chance to install it.

Just to annoy Matewis

Dawn of War

I believe I had beaten the game as Tau, Necron, Imperial Guard, but when I play the Space Marine, their Honor Guard was so underwhelming that I don't feel like continuing it.

It may be a balance because SM start with Deep Strike, so the dev nerf the Space marine honor guard to have a single unit instead of a gang of troops, you have no way of quick healing by buying reinforcement for the troops and with that low HP they dies easily, wasting your requisition. Other race honor guard is in groups and reinforce able, or if single unit is attachable to other squad or have high enough HP.

Final Fantasy 7
Replay this game a few times, then found out I miss out something I cannot get anymore after the stage. The closest I get is the crater to Sephiroth final battle, then would grind for more counter- mime material, then computer reformat, (i believe is due to crash)

Duke Nukem 3D

I've never finished the last 2 episodes to this day. I hate being interrupted by save/load screens in action shooters. So I was playing only using quicksave/quickload keys. No other save file. Stupid I know, but I was young and stupid. So deep into the 3rd episode (I think) i fell from a high place, went to quickload and accidentally hit quicksave just before going splat. Game over and I've never bothered to rectify since.

Honestly, I played it after Blood, Shadow Warrior and Redneck Rampage and wasn't that impressed by it compared to those others anyway.

Fallout 4

Soulstorm? The honor guard units in Dark Crusade are all single units for the Space Marines as well, but I can't remember them being especially weak. Granted I didn't really use them to attack much, except in really early in some levels. The terminator honor guard units were quite powerful though, capable of defeating low level squads by themselves.

Soulstorm did nerf SM from what I remember (one less weapon per squad + seriously reduced anti-vehicle ability) which, along with the unneeded flying units caused me to lose interest. The campaign levels themselves weren't that fun for me either compared to Dark Crusade.

Warcraft 3. Got to the last stage and just had enough.

I believe they nerf the Necro too.

I particularly love a turtling strategy of the Necro, rush multiple Necropolis to churn out free Necro warriors and march them to a choke point to die. delay your defeat with Nightbringer, captured fire prism, resurrected Tomb Spyder units and gauss turret. Then when you have enough dead you use Resurrection orb and from 0 units you can have 35 units. When they are all dead your nightbringer cooldown is ready, after then resurrect orb again.

Now it is a measly 24 units. And instead of yellow HP it res with red HP.

Ys Origin is great, haven't really encountered any crashes the few times I finished it.

Cool stuff thanks. I'll wishlist it for now, and keep my eye open for a sale/giveaway.
Had enough of the game, or the level? Because lol, that level is infamous. One of the tricks is to be pretty conservative with your two heroes' lvl6 abilities (tranquility(aoe heal) & starfall(aoe damage)), and only to use one during each wave. At least on normal it should then be pretty doable. I struggled for years though to beat that level on hard difficulty. Hordes of archers did the trick in the end.

Yeah, I'll never forget the first time I came face to face with a rising necron army during a multiplayer game. I was horrified! I had barely managed to fight them off when they assaulted one of my listening posts, and then suddenly all of them got up again and resumed their assault. If I hadn't managed to upgrade the listening post and equip some tacs with heavy bolters, I would've lost that match.
Necrons were pretty dangerous, especially with flayed one rushes, but the side I feared the most was always the Eldar.

I think it was the game in general and repeating the same levels too many times, and not really wanting to do that again with the last one.

Many.

I haven't finished last level of Thief 2

Thief 3, I stoped after Shalebridge Craddle. I think that's close to end game

With System Shock 2, I finished first Deck 5, that leaves me 2 level

Despite not finishing them, I still regard them as some of best games I ever played

That's just because you didn't get to the Rickenbacher and Body of the Many. If you're going to quit SS2 you chose a good place to do it.