Interesting story. I didn't get much use out of my Martian. I may not have made it far enough. Music could use a little work too :) Also, the fonts were hard to read on my box.
The game is ok, not bad but a bit generic. I think the main issue is the graphics (MS Paint?). Also, I'm not sure why the Martian is levitating on top of the screen, doing nothing, since you can restart with R. But everyone has to begin somewhere, so congrats for the effort!
So it looks like you can win the game in 5 levels regardless of which door your take. And the coins and the martian have no purpose, correct? For future games, especially Ludum Dare ones, make sure that you focus on getting a well rounded game over the number of levels. I have seen games on LD that have 2 minutes of gameplay and rank really high.
I think you have a nice concept here. Definitely plan out the purpose of the coins and the martian. It would be neat if you had levers or sensors or lasers up high that the martian could interact with while the man was on the ground. For the coins, you might need to get 20 coins (or whatever) before a door will lead you to a stage with a rock. You have a nice premise to the game with your introduction, but the story has no involvement in the actual gameplay. Work on these things (and the graphics, of course) and you will have a killer game on your hands. Good start and nice job finishing up a game on time.
Congrats for finishing your first LD! You've already beat 90% of people just by making something :) MS Paint graphics. Kudos on recording some music but it's fairly annoying. Gameplay doesn't make any sense to me.
P.S. Seems like it's your first Ludum Dare. Congratulations!