Day of the Tentacle : I actually think this is the perfect game. I love pretty much all Lucasarts adventures.
Earthbound : You'll have heard me talk about this game before. Well, it is the second perfect game. I love it to bits. I played it five times over the span of 2.5 months. I'm holding out on getting an adapter so I can play it on my PAL SNES and the wait is unbearable.
Timesplitters series : A nearly infinite amount of play time.
Sheep, Dog 'n' Wolf : A brilliant, inventive puzzling platformer.
Bugs 'n' Taz Time Busters : Best. Co-op. Ever. And hilarious.
DooM 2 : I used to play it daily.
Monkey Island 2 : I was bought this game a few months back and cried for the rest of the afternoon.
Super Mario All-Stars : The nicest, happiest, most nostalgic game collection. I had the pleasure of it being the first game I ever played.
Team Fortress 2 (360) : Come home from school - play. I never got bored of it, despite only having six maps and being as buggy as Hell. I find it a 'purer' multiplayer experience than the PC version. However, the class update came out and my patience started to thin.
Unreal Tournament : I will never uninstall this.
Quake 3 : Same as the above.
War§ow : The first skill based online FPS I genuinely loved. I remember meeting server regulars, learning how to strafe jump from nice people as I was getting lost on race maps, steamrolling n00bs, face, WDM2 and Padpork.
OpenArena : Equally important for me as War§ow. OA_SAGO 2 is THE greatest map ever.
Super Mario Land : I was lent this game for several months in primary school. I finally completed it a few days ago. (alright, I had to buy a new game. But it was still awesome).
Half Life 2 deathmatch : Illumi's Puzzle Server, where the Hell are you?
Sim City 4 : The greatest soundtrack ever!
FPS Creator/AGS Editor : got me interested in mucking about with games.
Eukaryote said:
Lego Rock Raiders: I spent many hours as a kid playing this.
Well crap, I remember renting that, it was great.
ExileNZ said:
Quake II, for all the countless hours I played it and its mods (most particularly the first 3 levels, over and over and over because the Warehouse sucked).
My first online game, and the first game I learnt how to mod.