The One Game... TO RULE THEM ALL

Hey guys, I have a question.  Out of ALL PS2 games you own/seen/played, if you had to recommend one and ONLY one game to a person, which would it be?  One that is just SO awesome, everyone (you think) should have a copy.  niche-games are okay too, since most of them rock anyway.

I suppose I would have to pick Disgaea.

>>10
I did not know Hyperzone was also a PS2 game, since that is the only system the OP is asking about.

Gonad...