Great presentation! Forcing the player to shoot in the direction they're facing made it challenging.
I liked the addition of the healing areas. I did see that more spawned on occasion, but I would have liked them to appear more frequently.
If there's a practical purpose to the additional ships that you can unlock, I didn't notice it. It would be nice if each ship had different statistics, but that might be too much to make during a game jam.
One complaint I have is that it was easy to be swarmed by ships and hard to recover from more than a few of them. It would have been easier if they had spawned less frequently. Perhaps you could then increase their spawn rates over time. You might also consider imposing a limit on how many enemies can exist at one time (or if you have already, consider decreasing it slightly). Again, this limit could be increased over time.
Great work!