Normal
It was a fun and addictive game (like every other 2d shooter). But you should fix so you can buy upgrades permanently and such. Because it's almost only luck if you make it. You will make it if you have good upgrades on the plan. A bit too many and too hard achievements thou. I got about 62 of them, after that i didn't have the energy to get all 78 :S. But a good game overall.
Keep it up