Hey magsolid!
thanks for playing! Thanks for noticing the powerup sound. At first I just had the power bar at the bottom, but I realized people will probably not notice when it runs out and could get pretty annoyed (especially with the shield).
As for the difficulty curve, the rate at which enemies spawn increases by 0.2 seconds each time a "skeletor" enemy spawns up until a new enemy is being spawned every second. You may have encountered one of the know issues with this prototype where less enemies spawng after each death. (can't fix because of jam).
And I thought I actually hit there and back better than collectables with this game because you're going around and round the black hole! I actually had a lot more planned for the collectables component but didn't get around to it.