Otogi 1/Otogi 2: Both receiving below the average of 82% is absurd for one of the best games on the XBox. Both games are brilliantly designed and well told. Unfortunately the original sold pretty badly, and I was shocked that a sequel was made but happen none the less. If you like hack and slashing with a little jumping here and there, this game is perfect. Oh, and even with the 360 out the game still looks very beautiful.
Bard's Tale: Crafted with the beautiful and addictive Dark Alliance engine, then add Cary Elwes for one of the most funniest video games ever (Maybe even over Conker) this game reeks of awesomeness. Unfortunately the comedy is probably the most enjoyable part, as even the addictive Dark Alliance engine can't save the repetitive and shallow combat. But this is underated just by the fact that Cary Elwes is a comedic genius.
Call of Cthulhu: It's really hard to describe it, kind of like a first person survival horror mixed with puzzle solving. Game has a rather large amount of twists, and wonderfully voice acted. Unfortunately the sequels were all canned as the company go KO'ed. Maybe not extremely underated, but underated none the less. Can also now be found on eBay for cheap.
Dungeons and Dragons Heroes: Diablo style hack and slash. Unfortunately the harder modes offered no extra experience. If this game had a online mode it would still be played to this day.
House of the Dead III: Lightgun made this game. Most people pass on it, but it was a great time waster. Hopefully the competition (Wii) takes off where the XBox forget to capitalize on and I see more lightgun games in the future.
Kingdom Under Fire: RTS/Hack and Slash heaven combo.Think Dynasty Warriors with brains. Really great series and cant' wait to see the pure hack and slash version coming to the 360
Kung Fu Chaos: Just ask around. Most will agree
Marvel versus Capcom 2: The most (or second most behind Steel Battalian) expensive game on the XBox. For good reason. This game saw ports from the Dreamcast version, but all in all is a perfect port with no online. One of the best VS games ever to this date, and only lowly rated because of no added features when it was ported (This was due to licensing issues, and is completely understandable on Capcoms part). Saw low production and was clearanced from CC long ago, then sold out everywhere.
Men of Valor: Run of the mill FPS that is actually pretty good. Had solid online back in the day.
Voodoo Vince: Ugh. So many people put this game down, and even less bought it. One of the best platformers for past gen systems, and unfortunately we will never see a sequel thanks to sales. Believe me folks, this is 100x better then B linx.