I was very impressed with the polish and artstyle of the game. The 4 levels that the game had seemed complete, but there are some features that should be added or changed for a better experience. It would be nice if there were any indication of when the charging cooldown was done, or alternatively maybe holding down the spacebar during the cooldown could automatically put you into the charging mode. Another thing is that if you try to charge upwards or downwards you are forced to hold spacebar and then pressing up or down, when it would be better if the charging direction started upwards/downwards if you're holding those buttons down when pressing the spacebar. The charging mechanic is pretty nice but it's a bit odd you can stay in the air indefinitively.
But overall a very good experience for what it is right now, and I would give this game a 8/10. Keep up the good work. :)