I really like this concept of working together to get to one place/goal. I like the way it plays. The gameplay is good & straightforward.
Music wise... well there is none. so a catchy background tune would be nice and maybe some sound effects for the moving platforms and jumping etc.
Also maybe a good transition between stages instead of just suddenly "popping"into another room.
One thing i definitely noticed was that the art for the characters and the art for the rest of the game is very different. maybe if you gave the background more color or something like that, it would look better. and the same art style on everything would make it look much more consistent.
Another thing, a very small tutorial wouldn't hurt... although learning as you go doesn't really affect you on anything, but i would've never guessed that they could basically jump on top of each other to reach higher places for example.
I gave this game a 3 star rating because although it is not finished, well it doesn't feel like it is anyway, the concept is really good and it was actually quite fun. hopefully you make it better and it comes out good. if you need reference on a game similar to this one try looking up this http://www.fireboynwatergirl.com
Its a really good game!! you'd do good to take something out of it :)