It's exciting because of the possibility for some really amazing user created content. It really is the youtube of platformers. Yes, there is a lot of crap being published for it right now, and there is a small percentage of really quality levels. Azure palace is awesome, the sackhouette couple of levels just look cool, and are decent levels. It's just fun.
I'm already not liking the mechanic some people are using, you can basically hit a fire hazard once without dying, I'm getting really tired of seeing levels that force you to bounce across fire to make the jump to the next bit. I would be ok with using that mechanic for getting to a secret area, but not as a repeated level mechanic.
It's just a fun bit of software, a solid platformer with multiplayer, and all the tools to create whatever you can imagine. For those of us that love fiddling with things, this is a great game.