It reminds me a lot of Contra: Hardcorps wich says a lot of good things about your game. I think having checkpoints at least on the easy difficulty wouldn't hurt too much. Gameplay is excellent and the graphics are nice but also have room for improvement. I'm already waiting for the next demo! Great Job!
Thanks for playing! I'll likely add checkpoints at some point, planning a "story mode" of sorts in addition to arcade mode anyway. Art is definitely my biggest weakness.