I absolutely loved this game when it came out.
Shadow Of The Colossus
I loved this game on the ps2. The enormous enemies and environments and the overall atmosphere of the game just felt unique and adventurous.
Grand Theft Auto San Andreas
Vice City was a blast but San Andreas really opened up huge possibilities in the game. There was soooo much you could do. I probably played this game 2 years straight without even touching another game.
Metal Gear Solid Snake Eater
The 3rd person camera view made this series even better for me. Also, there was a relatively decent level of realism for stamina, bandaging wounds, enemy AI, and shot detection (where the attack hit on the body). The story-line was pretty fun (recycled but fun) and taking on Big Boss at the end was an interesting challenge. (MGS2 had a better story though
)Final Fantasy 7
Yes it was cheesy. Yes the graphics are dated. Call me crazy but I loved the strategy, story arc, and epic feeling of the game.
Final Fantasy Tactics, Ogre Battle, Vanguard Bandits, Battle For Wesnoth, etc.
I've been a sucker for turn-based strategy games for a long time.
DOOM
Classic awesomeness!
So yeah... I can't pick just one that's my all time favorite but these games would certainly make the list. Newer games have more polish and fancy features, but these older ones made a long-lasting impression.
Was once ranked 9th global on Xbox Live 
looking forward most to multiplayer jets. Also looking forward to SWTOR release, it looks like it could be one of those "revolutionary" MMORPGs. I guess we'll never know until it hits stores.
