I'm going to follow the thread title and say what game made me go "WOW", rather than what i just played a lot or thought was good. I have a horrendous memory, so i've been reminded by some by this thread, so i'm trying to think of old games too, but it's hard, i can think of 7:
7. Goldeneye: Perhaps my first venture into competitive multiplayer gaming, where i would compete in magazines, so maybe deserves higher. The game was why i got an N64
6. COD4: Amazing storyline and execution, the ending was immense. Left me saying WOW, as well as my dad.
5. Donkey Kong Country: Best graphics game on the SNES, loads of replayability and the gameplay and graphics wowed me.
4. BF1942: Another game my dad played a lot, though he couldn't get to grips with flying

. Awesome game, it wowed me how i could drive anything and fly about at will.
3. WoW: Anyone who's played MMO's has got to give the game credit for doing everything good, but nothing perfect. Everything was fun, which is whats important.
2. Planetside: BF1942 but on a grand scale taking over continents and bases MMO style, enough said.
1. Star Wars Galaxies: No game has detached me from the real world like this. It was a real world in itself, felt life-like and truely magical. Never before have i had such wonder, having a feeling that there was this much bigger thing in the game i had to discover, that there were mysteries i hadn't uncovered. The mystery of jedi and such really captured a childlike wonder that i doubt i'll recapture. I can look straight through most games nowadays, inside out i know them and could say "i know how this was done", but SWG always had me wondering...