A few things to say, I have downloaded it but have not gone far as the character select screen. I've seen (most) of your dev logs and it is pretty epic. (these are suggestions)
But i cant play with anyone, because there is (i'm pretty sure) no computers to play with. You should make computers and have difficultly levels.
And last, make different game modes like the one you have now, lets say "original" and another game mode stock where you have 1-6 lives and if you fall off you lose a life and there is no 30 sec countdown for the spikes to come out. (And make this customizable) But overall I really love this and I will play the full version.
Edit: I played with my brother, really fun!