1.) Tekken3 (arcade) - no other game has come close in # of hrs spent playing and studying this game
2.) Starcraft (PC) - the best RTS ever; still play it now and then
3.) Wing Commander (PC) - the original was truly groundbreaking; and with a Roland MT-32 for audio, it was the first cinematic experience I had with a game
4.) Planescape: Torment (PC) - best story ever in an RPG, and great gameplay as well, all set in a fantastic D&D setting
5.) Grand Theft Auto 3 (PS2) - wow. Really changed my impression of console games.

1. Ms. Pac-Man (Arcade)
2. Soul Calibur (Dreamcast)
3. NHL 2002 (PS2)
4. Super Dodgeball (NES)
5. Tony Hawk's Pro Skater 3 (PS2)

Right at this moment:

1.Metal Gear Solid 2:SoL (PS2)
2.Super Mario World:Super Mario Advance 2 (GBA)
3.Baldur's Gate Dark Alliance (PS2)
4.Virtua Tennis (Dreamcast)
5.NFL2k2 (PS2)

1) Syphon Filter (1-3) (PSX)
2) Tony Hawk's Pro Skater (1-3) (PSX- PS2)
3) Mike Tysons Punchout (NES)
4) Tie Skate or Die or 4th and Inches (C64)
5) Double Dragon (Arcade)

Also up there

Metal Gear Solid (1 and 2)
NBA Live Series
Metropolis Street Racer.

This was harder that I thought so I cheated and used a few series
(in no special order)

Super Metroid (SNES)
MGS 1&2 (PSX, PS2)
Medal of Honor series (PSX, PC)
Tony Hawk series (PSX, PS2)
GTA3 (PS2)

My top 5 are...

1. Street Fighter 2 The World Warrior(Arcade)
2. Mega Man 1-6
3. The Legend Of Zelda - Link To The Past
4. Chrono Trigger
5. Super Mario Brothers 3

Myth--PC

Half-Life-- PC

Romance of the Three Kingdoms--SNES

Secret of Mana--SNES

Wizardry--Apple II (probably what got me hooked)