Pretty fun game. I think the variety in levels was more or less enough to hold my attention the entire time... just the different rearrangements of black holes and platforms was really enough for how short the game is.
I thought the physics were a bit finicky... sometimes the black holes would direct me the opposite direction I expected, and sometimes I would get confused where exactly I should place my mouse to change the strength. (I think the mouse center suggestion is a good one).
Somehow when I first went through the tutorial I ended up thinking we were supposed to click on the screen where we wanted the player character to fly towards, as that's essentially what I did to complete the tutorial. Not really a real problem, just an interesting phenomenon.
One nitpick: I feel like the fire might look better if the texture was drawn at its maximum size and then scaled down (or, if necessary, have a couple different textures for different scales). Not a huge deal, I just tend to think consistently scaled pixels look better.
Overall though this was an incredibly solid entry. The game was fun, looked good, and sounded good.