Pah, those games aren't even in the same league of under-ratedness I present;
- Psychonauts. Pretty much my go to answer for this question, a game of true originally, great story telling, funny script, and genuinely well developed characters. Raz sneaks into Psychics Summer Camp after running away from his father and the circus, but someone is stealing cadets brains....
- Sheep, Dog 'N' Wolf. I will mention this game until the end of time so more people get to experience it's joys. A platform/puzzler based around the old and not well heard of Looney Tunes cartoon, Ralph Wolf (Wile E. Coyote's cousin) has to still sleep from Sam Sheepdogs flock as part of a game show hosted by Daffy Duck.
- Kung Fu Chaos. Multiplayer beat em up where you take control of one of a variety of Kung Fu characters in order to film the latest Kung Fu movie. Not your traditional beat em up, as the background and fighting area constantly moves around as you film that particular scene for the movie. Really good fun.