I just purchased and completed Ape Escape 3 for the PS2. Pretty good platformer that gets tedious at times and is way too freaking easy, but well worth playing. I'll be damned if I'm going for 100% completion though.
Right now I just bought and started playing Shinobi for the PS2. I mainly bought it because I'm a fan of the series and I read that it might well be the most challenging game on the PS2. If you've read any of my posts on this board you know I love a good challenge, and, although the game is certainly challenging, I can't quite decide if it's any fun. Difficulty is fantastic, but the fun needs to be there too.