Congrats on the first jam! As with most first timers the game is a bit rough around the edges.
Let's start with the obvious. A game about a punk skeleton (the concept I personally love) needs a punk-rock soundtrack! There's a bunch of free music you can find, and this game would really benefit from having it!
The skeleton, cops and the city looked ok- no notes here.
As for the gameplay- when making the game for the jam make it easier than you normally would. Some of the people won't be familiar with the genre you are making and you want to make a game that appeals to a broad audience. In your game I got stuck at a vertical jump. No matter what I do I can't get enough speed to get that high. The idea is cool- but some playtesting would help.
One more thing. I think this is pretty ambitious ideat for a 4 day jam. Time management is the most difficult task in a game jam, so my advice is as follows. Cut the time in half. Think of what you can do in that time. Then do it, and you have the rest for polishing and bugfixing.
So to sum up- good idea, but needs some difficulty balancing. And a punk-rock soundtrack.
But what DOESN'T need a punk rock soundtrack, am I right?