Well, for a simple platformer jumping game (I haven't seen this before), I actually liked it. It looks like some way of choosing how the story goes, but seriously, Animation was clunky and the smooth surfaces weren't so smooth. It looks like this was drawn in MS paint with dragging boxes, but thats just my opinion. Good work, though.

The jumping is decent and it reply's decent but only 1 lvl as a demo?
The falling-lvl doesnt lead to anything yet :) and the way you build it you can imidiatly go to the boss, make some kind of obvious blockage here :]

Found out by luck that "d" extends a arm or smt...

I give two stars because normally games like this are either A. Completely designed to be pointless and stupid, or B. are actually works in progress, and i see this is the case with you.
Things to fix in the future;
A more original sound track (i am trying to help you on this one as Copyright guys have demanded take down notices for less)
A more precise control, the double jump has a tendency to activate while I am jumping, leading to many unwarranted fails.
And from what i read from below, random falls into the abyss are never a good thing.
Lastly most of the blocks have consistency issues in there designs, parts just stick out more here and there.
All in all keep it up and i am sure this will be good.

the spikes are way too sensitive. i would go anywhere near them and not even touch them and still die somehow. that needs to be fixed

Sorry buddy but this gane,ehh,i see a good future for it but first...get rid of the random falls,i fell into blackness several time becaus eof random spots,also have some hints at the beginning or in the description i was really confused,also add diffirent backround music