Made it to level 12! I had a fun time with this one even if it gets a bit repetitive after a while and the only real difficulty scaling is the addition of more planes. Maybe something to expand on is the addition of new plane types that fire differently or ground turrets that target the air.
I'd say my biggest complaint is the lack of a health bar. It's hard to gauge how careful I need to be about getting attacked without any idea how close I am to exploding. I noticed after reading some of the other comments that the smoke color changes, but I don't know if it's apparent enough to warrant no health bar.
Besides that, I will say that the little arrow indicators for the artifact positions are very well done and super helpful!
Also cool to see how someone else used the same tileset in their entry :)