Fun, challenging, and annoying. I had a lot of fun with the game, and a lot of the medals were fairly good ideas.
I have to say though, the characters voices were f***ing horrible. I felt like I should be offended somehow. You give the option to turn the voices off, which would make up for it, but then you throw in medals that require the voices to be at maximum.
I found both control schemes rather awkward, but given the variety of movements I can't think of anything that would be wholly comfortable. The ability to switch characters with the numpad's 1,2, and 3 keys would help, and making 'quickswitch' the right mouse button might also have been helpful.
The gameplay and puzzles were rather good, though in the levels were you have to use 'Yeah' heavily it got kind of awkward, I could never get him to aim properly.
Also, some of your challenges were just INSANE, apparently (judging by highscores) I am one of only 8 people who was able to get the 'Master of the Universe' medal (which I admit does have a suitably impressive title.) Several of the medals for individual levels seemed undervalued as well.
Also, when I played this the first time after I beat the game and selected 'quickplay' back at the menu I entered the mysterious 'Level 0' I didn't play it at the time, but since then I haven't been able to get back there. What was that all about? Does anybody know?
Oh, also, WTF was up with Mr. Secret? It just came out of the blue and didn't bear any relation to anything else in the game. I'd been playing a fun, happy-go-lucky, yet frustrating platform game. I make it through 'Oh Love' which I was sure was the last level, then all of a sudden, BAM! One more easy level, with wrong sounding music and a giant f***ing eye in the background. Not really the scariest thing, but in this context holy cow was it startling. Seriously though, what was that about?
Still, overall it was very fun, even if it was very challenging (and bizarre).
P.S. Your tutorial kind of sucked. I'm all for letting the player figure stuff out on their own, but those background images were just kind of dumb.