Disclaimer:
I'm 16, and grew up playing video games, starting with the NES. I have every mainstream system made up to date, and a few non mainstream ones (anyone ever played teh NEC TurboGrafx 16? Or the Atari Jaguar). So, that being said, you'll notice a lot of my favs are older ones, cuz you just can't beat the gameplay. Too many games recently rely on graphics alone and have lame-ass story lines. And yes, I have played the oldschool ones recently so I know I'm not just glorifying the good old days. Oh, and 15 just isn't enough!
By Systems
Nintendo:
NES:
CONTRA!!!!!
Original Mario Bros
Jackal!
Duck Hunt-just cuz its fun to shoot with the gun 2 inches away from the screen!
RC Pro/Am
SNES:
Mario All-Stars
StarFox!!!
N64:
I suppose Mario 64
Mario Kart
Bomberman 64
GameCube:
James Bond Agent Under Fire
NFS Hot Pursuit
SoulCaliber
Sega
Genesis:
The Original Sonic!
Saturn:
Daytona 500!
Sega Rally Championship
Virtua Cop 1 & 2
Virtua Fighter
DreamCast:
Sonic teh Hedgehog
Tokyo Extreme Racer!!
ReVolt
Crazy Taxi
There are more for this one, I just cant think of em...
Microsoft
XBox:
Halo (Halo 2 SUCKS)
Apex
SplinterCell-all versions
Ghost Recon
Rainbow 6
Midtown Madness 3
TOCA2
Sadly, I don't have the 360 yet
Sony
PS:
Twisted Metal! FTMFW!!!
Gran Turismo Also FTMFW!
Crash Bandicoot
XGames
PS2:
Gran Turismo 3 & 4
Ehhh...thats mostly why I bought the PS2
Others
NEC TurboGrafx:
Bomberman '93!!!!
There are more, my mind just went blank. Oh well...
Atari Jaguar:
Pinball!
Raiden!
The Snowboarding Game (can't think of name)
Some really cool outer space game (had some freaky green face that told you stuff in a weird voice)
Special Mention:
Initial D 3
Galaga/Galaxian
And, I really don't do computer games that much, but DOOM 2 deserves a special mention. (Yes I played that when I was 5, I don't think it made me *too* demented
I know I'm forgetting lots of games (and prolly a few systems too) but thats more than 15 anyway!