Ion Flux
Savant
I've been playing it for free on Gametap and it's probably the most fun I've had playing a game in a long time. It reminds me of what Disney World would be like if Tim Burton and Roald Dahl designed it. I've actually been playing it with my seven year old daughter and it's a blast. If you haven't played it, I highly recommend this little gem. Get it while you can for free!
Edit: Oh, be warned, it's an adventure game, but it's also a platformer. However, I tend to not like platformers due to their obtuse and irritating jumping puzzles and stuff, but this one really integrates the two genres well. I find the jumping puzzles to be far less annoying than other platformers, so even if you hate these kind of games, this one is still worth a try.
Edit: Oh, be warned, it's an adventure game, but it's also a platformer. However, I tend to not like platformers due to their obtuse and irritating jumping puzzles and stuff, but this one really integrates the two genres well. I find the jumping puzzles to be far less annoying than other platformers, so even if you hate these kind of games, this one is still worth a try.