Gotta go with Tecmo Super Bowl!!!

The game that really did it for me was FORSAKEN.  It was the first Glide based game designed for 3Dfx Voodoo Cards!  The fire, graphics, and everything else was simply amazing compared to DoomII and the like!

Hell yes. forsaken was probably the first real 3D game I've ever played on the PC.  I remember i was running it on a PII266 with 64megs of ram and an old riva 128 w/4mb of ram.

Quake 1 on a service called MPlayer any of you old heads remember that? Capture the Flag mode. Rocket jump FTW =)

hmm Mplayer. I had used that when playing MechWarrior 2. I remember it being very annoying.

Yeah voice over IP was new at the time and that saved many people teh $$ even if they didn't want to play the game. Gah, I remember that was when I started looking into Linux/BSD and still it doesn't get the credit that it deserves.

Hmmm....of all time.  I am defaintely going to have to seperate these into different systems.
Arcade: TRON: Deadly Discs - 'Nuff Said
Atari 2600: Yars Revenge
Colecovision: Wing War - one of the weirdest games with no music, no storyline, and pretty much no rhyme or reason except to collect eggs and jewels as a 4 bit fire breathing dragon.
Nintendo:  Blaster Master - hands down one of my alltime favorites.  Too bad there were no saves for the original systems.  Thank gawd for emulators and state saves.
Sega Master System:  3d Missle Defense - One of the BEST 3D glasses systems EVER, and you played with a light gun!
Sega Genesis:  Sonic (all of them except sonic and knuckles)
Super Nintendo:  Super Metroid - The best in the series IMO
PS1:  Vagrant Story - Best RPG...EVER
Ps2:  GTA: San Andreas
N64:  Goldeneye - I have stayed up countless hours playing 4 way DM's with my friends...and enemies
GC:  None really, except RE:4 but the better version came out for PS2
 Current gen consoles - I haven't decided yet.

I almost forgot!!!! 
PC:  There are so many! But I'll limit it to the top 5...

1: Quake - it's what got me into FPS's (well fully 3D fps's - let's not forget about Doom and Duke Nukem) and where I learned all about the wonders of the WASD
2: Carmageddon - Carpoclypse Now,  theres nothing like slamming a fully damage modeled super car into a bunch of bloodied pedestrians and hearing them go squish. And then replaying it over and over and over.
3: Battlefield 1942 - the game that changed the face of online multiplayer FPS's
4: Sam and Max - One of the Funniest adventure games ever.
5: Maniac Mansion - see above

Tribes!!!!!!!! how bloodshot were your eyes man... oldschool FTW!!