My health didn't visually deplete, I thought I wasn't taking damage at all until I died. Also, once you get game over you can't replay the game as it just takes you back to the game over screen, you have to close and re-open the program.
The base weapon seems powerful enough to not need to merge with anybody, as I could just mash spacebar to kill everyone onscreen and gain my health back immediately.
The AI on the allies is a bit off, too - they find it difficult t o be around me sometimes, which hurts.