Here is a partial list of games I consider awesome. Partial because it's hard to remember everyone of them
Partly stolen from other people here because I noticed I forgot a few awesomes.
In no particular order: (actually, in completely random order)
Dominions (3&&2) - Not much more to say.
Warlords: Battlecry (2&&3) - I'm not very good at it, but it's definitely a fun game. Quite unique too.
Dwarf Fortress - It's Dwarf Fortress! Need I say more than "dwarves going berserk after drinking water tainted with the blood of their recently murdered wife and newborn child"? Maybe I'll say "beating a skeleton to death with his arm" to the rogue crowd
Dungeon Keeper (1&&2) - Classic. How can you not love a game where you get to slap little imps around with a gigantic hand?
Infinity Engine - Is the engine upon which many awesome games are based.
Galactic Civilizations 2 - A 4X game with none-sucky AI
Civilizations 4 (somehow I didn't play the previous ones) - Great. I especially like it with the Fall From Heaven mod.
Red Alert (1&&2) - Sure, they aren't too smart, but they are a lot of fun. If I still had my RA2 disk(2) I'd probably still be playing it. At least occasionally.
Heroes of Might and Magic - 2 is my favorite, but 3 is awesome with WoG and 5 is nice enough.
Starcraft - One game that I don't enjoy playing anymore, but I had so much fun with it in the past that it is definitely worth mentioning.
Tyrian 2K - The big daddy of shmups.
Raptor - The big... mommy? of shmups.
Scorched Earth - MIRV! There's even a modern (free) 3D version that's quite a lot of fun to play online. (I stopped though)
Golden Axe - I get to play the dwarf! (or the puma-man-thing in the newer[est?] version)
Monkey Island (1 through 4) - From back before quests were extinguished
One Must Fall - I used to hate getting beat up by an enemy that was just pressing random buttons >_<
Mortal Kombat - Not fun these days, but deserving of a mention.
Worms (all the 2d ones) - Boggy B fell in the drink.
Warcraft 2 - Sorry, but 3 was no fun at all.
Diablo (1&&2) - I don't think I've ever finished any of those games. Still a lot of fun.
Age of Empires (!3) - I heard 3 was lame and never bothered with it. The rest are lots of fun
C&C - The original
Duke3D - Hoo boy, I spent lots of time on that one.
Unreal Tournament (classic and 2k4) - I've some pretty awesome moments with those.
Deadlock 2 - w00t! An Accolade game
Hitman: Bloody Money - And what a great finale.
Carmageddon (various versions) - You get to race, blow cars up and run over people and animals, what else could you want in a racing game?
GTA (various versions) - Because nothing beats delivering a bus load of people to a factory to be turned into hotdogs.
Toribash - Beating someone to death with your own dismembered arm? Where do I sign up?
Tremulous - An online shooter with base building where aliens fight against marines.
Counter Strike - I'm not a 1337 kiddie, I swear.
Dear Avenger 4 - Hehe, hunting people as a dear.
Dungeon Siege 1 - Because I finished it with my brother.
Empire Earth - You can't deny that it's fun.
Gazzilionaire Deluxe 2 - A hilarious space-trader game.
Theme Hospital - Where you can cure people by popping their inflated balloon heads with a needle and then reinflating them to a proper size.
KKND2 - Mutants VS Humans in a fun strategy game.
Little Fighter 2 - I even spent some time modding it.
MDK 1&&2 - If you haven't played these arcade(ish) shooters you haven't played any shooter.
Total War Series - I don't think I need to say much.
NetStorm - I just love the concept of fighting with buildings. Even in RA2 I'd occasionally defeat the AI by building a huge line of Grand Cannons all the way to his base
Populous: The Beginning - I just love the way they repeatedly jump up and down on the ground to flatten it before building on it.
Soldat - I was pretty good at this one.
Startopia - A sim game where you build a space station, how cool!
Total Annihilation - A serious hole in your education if you don't know this one.
Many other games I'm sure I've forgotten
- I'm really sorry, games
Though of course, the best of all games imaginable is the (crappy) ASCII (somewhat roguelike) game I'm programming now
(still very far from a playable state)
EDIT:
Endo - NWN is meant to be played online, on specially created worlds/adventures (quite often with very big mods of their own).
I played a bit with the original NWN, but when the expansions came I was forced off because I didn't feel like purchasing them, and all(most) games now required the expansions to play.
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