Interestingly, I came here to post Gamepro's "Ten Underappreciated Gems." Might as well do it here, as it seems to be basically a similar list:

1. Ico (PS2)
2. Poy Poy (PSX)
3. Beyond Good & Evil (PS2)
4. Incredible Crisis (PSX)
5 Katamari Damacy (PS2)
6 Adv. of Cookie and Cream (PS2)
7. Mad Maestro (PS2)
8. T2: Judgement Day
9. Typing of the Dead (Dreamcast)
10. Zombies Ate My Neighbors (SNES)

Let's ignore the fact that the list is pretty Sony-centric. Let's also ignore the fact that several of these were released for more than one platform. I'd have to agree with several of them as being underappreciated. BG&E, Incred. Crisis, and Typing fo the Dead to be sure. But Katamari? Sorry, an "underappreciated game" does NOT get a sequel. And T2 is underappreciated? Hell, that arcade game was released for virtually every system I can think of - including the Game Boy! "Underappreciated game" does NOT get released across a shitload of different platforms.