Thank you for playing and your suggestions.
About the jump indicator, I agree. I wasn't particular happy with it in the end and others complained as well. I intend on improving this after the jam (if real life lets me).
The black hole was a frustration of mine. I intended to introduce the same dialog I had at the beginning every time a new hazard was introduced, just to give a tip on how the hazard worked. The final levels were also not what I've liked. In the end I just hadn't enough time and went with something that worked.
The sling control doesn't have a defined radius, you can click anywhere on the screen. I can't blame you for not knowing this though, again, no time to create systems to teach the player how to play the game. One suggestion some other player gave me that I liked is to place a marker where you started clicking, making it easier to judge direction and pull strength.
Nice suggestion about the air meter. I confess that mechanic didn't have an official name as it was a fix for an issue the game had. At a certain point in development the black hole could lock you into orbit, basically soft locking the game. I added a "time in air" mechanic to avoid that and liked it as an added layer of difficulty. I intend to improve on the timed aspect, maybe even adding an overal timer and a speedrun mode.