Now I don't write reviews all too often however I feel that since I am starting to make my own flash games that I might as well start sharing my opinion.
1) No by no means do I mean make the game real in every aspect however I feel you may want to think about your gravity value as jumping and falling we both rather slow which can put people off a game, especially when it comes to dodging enemies.
2) Make it clear that you have to actually dodge the things coming accross the screen. Also on some of the levels the enemy would kill you just after the start of the level as you havn't started moving. It also seemed they were on a continual loop...Using Math.random() along with + and * can add some variety to it as it is unknown where the enemy will come. You could even use something simple like Math.ceil(Math.random()*2) to make it come from either the right or the left (Math.ceil() making the number round up so 1 or 2 are the outcomes)
3) I use a desktop computer however did use a laptop for quite some time. Having the ability to choose to use AWSD or Arrow Keys is usually a vital component to games as it allows for players who are left handed or right handed without having to have hands crossing over each other.
4) Having levels that scolled as you went through the levels would be good or basically zooming in on the player a bit more.
5) Lastly you may want to take a quick look at your lives as it said I was on 0 all the way through the game.