I know this is still an alpha and all but I'm still going to give my two cents.
The momentum feels kind of unnatural. It's hard to explain, but it feels like instead of conserving the movement the jetpack is trying to hit the brakes but it still takes a bit to fully stop. Like an old car, know what I mean? Now, if this is intentional then by all means keep it, this is your game, not mine.
Other than that I see that you have the core gameplay down, so all I can suggest is maybe more stages or enemies or something (?). I dunno, I suppose you already have those in mind. Either way, this looks promising. Keep at it!