It's a solid start
I like what I see so far.
I want to complement you on the graphics. It looks great, has a lot of detail and defiantly draws me into the game more.
The basic gameplay is fine, but I do have a few suggestions.
I didn't like that I had to hold shift to run, and walking was too slow. I would suggest that either you make it so that you are always running, or make SHIFT toggle whether your in walking "mode" or running.
Personally, I think that the character falls too slow, and made jumping from platform to platform too easy and slowed the game too much.
It would be awesome to have some power-ups or items to use for different things
There should be more obstacles, I know you already said that there would be more in the final game, but I just wanted to emphasize how important that will be to the game.
There is a rather annoying problem with the program, sometimes when you land on a platform you bounce up and down a very small amount continuously (it gets really annoying after a while). In a related problem, you can fall so that you land half-way into the ground (you can still jump out), or one time I fell straight through an entire platform.
Well, good luck! It looks like its going to be a great game and I look forward to playing.