Got to level 8, not too bad! Couple of things I did notice, tho:
- As someone with no blood type knowledge, it was pretty much trial-and-error to see which blood types hurt me and which ones didn't. It's probably intended that you know about blood types before playing, so it's not that big of a deal :P
- Once the little blood barriers spawn, it's easy to forget which blood type it is - especially in later levels with barriers being more frequent. Maybe add the letter inside the barrier?
- A little warning icon of where the projectiles are going to be shot from would be pretty nice, just to have some time to react
Overall, I really enjoy the concept! With a bit more polish and variety you'd have an addictive little game for sure. And the music is a banger.