1.) Ratchet and Clank III: Unlike the other games, this one had the most replay value. I actually completed the campaign a second time. Not to mention that it had the best weaponry

2.) Super Mario 64: The first game I ever played as a kid; it wasn't until I got a PS2 for christmas that I stopped. It was that good. I got all the secrets, which I rarely fully succeed in doing, and it could be played as a family rather then just me in the special entertainment room.
3.) The Sly cooper series: Yeah I know I'm cheating, but I just really liked this series. The characters, worlds, and gameplay were all made, and while the first game has outdated graphics, it still holds a place in my heart.
4.) Knights of the Old Republic: I got this 4 years after it came out, and it was still really good damn cool. I can't really say anything that hasn't already been said, just that playing as all lightside is still really cool (I am just not able to make a dark side action.

5.) Paper Mario The Thousand Year Door: This game is awesome. I liked it, and it's one of the few I bothered replaying. The replay value is that good. It's bright, colorful, creative, and fun for all the family.