I think the voting has been harsh on your submission. There is alot of positives in your game. For a first game its actually quite strong. A lot of gamer's like an intro menu and instructions, which you should add to your next game. If you go into the project system for this game, you can edit the Author comments section and put the instructions in there, a lot of other devs do that for small games like this.
I actually liked the way the game handled, the double jump had a nice feeling to it. colision detection was also very good. I think you should make a version 2 of this game. If you replaced all of the bland visuals with some nice pixel art, add audio for the jumping, add a menu etc and re release the game you will get a much better score.
Great first game, obviously it can be greatly improved, but A+ for effort. Making games is not easy ;) keep up the good work and keep increasing your standards.