Wow everyone has some pretty awesome picks, as for my pick of the list though I chose Assassins Creed II thought in all honestly I would probably dump it and its sequals onto slot numer 7, so my top 5 favorite games are:
1rst- No More Heroes- I loved this game kickass main character, awesome music and a zany story that is just impossible to get tired off.
2nd- Persona 4- I pick up a lot of jrpg usually its pretty rare if I ever get around to finishing them due to my busy schedule but Persona 4 was one that I could not leave alone for long I loved the story I loved my party and I remember it fondly.
3rd-Knights Of The Old Republic1&2- I can never decide which I liked more 1 because of its awesome story, and characters, the as for number 2 due to its awesome interface and characters and deeper philisophical aspects of the starwars universe it explores. I loved kotor 2
4-Catherine- I actually enjoyed this game enough to play through it 4 times when my normal number is 1 or 2 so if that doesn't say I liked the game I dunno what does.
5th-Portal 1&2- This is a pair of games that I cannot split apart seeing as how I liked them both equally, I normally avoid puzzle games but these 2 were to entertaining to ignore.
Honorable mentions include in no particular order: Kingdom Hearts Birth By Sleep or 2,Dante's Inferno, Dawn Of War Retruibution, and Devil May Cry 3.