Soviet Heavy said:
Halo 3 ODST. Much better than Halo 3 be sorely under appreciated.
I wouldn't call it under-appreciated considering it was freaking halo, but it IS far superior to Halo 3. I loved the original Halo, but couldn't stand Halo 3. At first I thought it was okay, but now I've soured on it to such a degree it has officially become the only Halo game I hate.
My pick is probably Urban Reign. See, most of you have never heard of this game, but it's the best 3d brawler outside of God Hand. Actually, it is to multiplayer-focused brawling what God Hand was to the single player side. It's deep, technical, easy to get into and looks quite nice for the platform (PS2). Urban Reign is also tough as nails on any setting higher than Easy.
Two other underplayed titles are Oddworld: Stranger's Wrath, a brilliant game that none of you played (which is why Lorne Lanning was basically driven out of business, thank you very much), and The Punisher, an awesome third-person shooter with intuitive controls, a pretty good story, classic Punisher (Garth Ennis era) characters and designs, tight shooting and the ability to torture enemies for information.