Enjoyable game, but a bit too easy. I got over 10,000 points before I decided to end it. Some things you could adjust would be the damage of the enemies, or how long you can have the gravity well activated. There is no reason you shouldn't have it on at all times. Putting a restriction on it would introduce another level of complexity which I think would help the game be more interesting to play for longer.
Good luck in the jam!