for me:
BioShock: i remember picking this game up at BB, started playing at around 6pm i got home and just played, there was a point where i just knew i should put it down, i looked at the time and it was 1:30am!!! i had made it all the way to fort frolic!!finishing the game i gave my self i nice pat on the back... i love this game so much
God Of War: all the combat/puzzles/story IMO, i gave myself a HUGE pat on the back finishing this game was really satisfying, huge sense of accomplishment.
Mass Effect: once the story got going i just wanted MORE!!! the side quests were a snooze fest but the main story i havent played anything like it.
MGS4: OMFG!, the only thing that messed it up IMO was the end cinematic, WTF! i think i got up made myself dinner came back and it was STILL ending.
