it's a nice game, thought I stopped at level 13, because either the game or my computer has problems, but since I don't know, I'll blame it on my computer, because sometimes the keys didn't respond properly
so therefore I'll judge on the levels I've done so far:
I think the game is very nice and challenging,
though I kinda miss a story line, as in, why is he trying to reach the end of the levels, how comes he's able to change gravity, which costs you a half star
music starts to be annoying after a few repeats, though you do have a mute button, so it costs you only a half star, instead of one
I like the retro looks, this game is a good example that retro isn't always bad looking
I also really like the fact that you can get help in the first couple of levels, so it can kinda function as a tutorial for the ones who need it, but if you think you are able to do it yourself, you can choose for that as well, a very good solution!
overall, I think this game deserves the 4 stars, improove the music (by making it less annoying) and add a little story line, and you could get 5 stars!