I am wondering if I should get HoMM3, but I prefer the slightly better graphics of HoMM4 (which oddly isn't available at gog?), what does the third one have that the fourth one doesn't have? I read somewhere that the factions were changed?
I played both way back in the past but I honestly can't remember why HoMM4 was said to be worse than 3.
I have 5 but I just can't seem to get as enthusiastic with it as I was with the older games.

Off the top of my head:
-units (and factions in general) are mixed
-every faction (except Might, ofc) has its own school of magic
-hero skills are changed to 5 ranks and they are divided into primary and secondary skills (f.ex.:combat -primary, melee, ranged, magic resistance-secondary skills of combat)
-no automatic firing turrets in siege and no catapults to destroy walls
-buildings like windmill generate resources automatically every week, if flagged
-monsters appear in dwellings over week and not only first day of a new week
-fog of war on adventure map
-no hexes on combat map
-monsters can wander without hero and you can have multiple heroes in one army
-caravans
-more obelisk treasures on map (and it can be more things, not just grail)
And more that I forgot about.

Really, HoMM 4 is a completely different game from HoMM 3. Although the basic idea is the same and the gameplay flow is the same, the implementation is huge. Good HoMM4 players usually make the game into D&D by having entire parties of heroes, which makes the gameplay much different (and it is also why HoMM 4 is generally considered inferior to HoMM 3 by most fans).

Funny. I thought it was because it had no AI and was just a pretty bad game, inferior in every single way. Unless of course everyone who thinks that is wrong and delusional and we need you to tell us that we're wrong and that you're right?

Dude, what the hell are you doing? Not only is this post from four years ago, you are also just blasting someone and adding nothing to the conversation. You're making an absolute ass out of yourself.

+1

I will have to agree though that 3 is quite a bit better than 4, and that one of 4s downsides is it's AI. Problem is that it is a 4 year old post your necroing.

You gained a level in Necromancy!