hmmm, the games that have made me go "wow" the most..not necessarily the most played, but the ones I remember the most.
For me, that would probably be:
PC: Call of Duty (1). Installed it, started playing, finished playing in one sitting. I was completely addicted to the sheer level of immersion that the game provided. Sure, it was kind of on rails and not a "thinker" by any means, but the level it made you felt like you WERE in an absolutely whirlwind of combat in some scenes was unprecedented.
Console: Metal Gear Solid. I'd say the 1st, but the 4th is up there too. I loved the way it was shot (I say that like it was a movie

), the pace, the story. Sure, a lot of people give it crap for a convoluted storyline and long cutscenes, but it tugged at the movie watcher side of me yet still gave it entertainment. Definitely enjoyed every minute of it (okay, almost every minute).