The waves come very quickly, even on Nooblet. I struggle to reach level 50 only on Nooblet, I don't even try harder levels. Suggest more time be given between waves.
After playing the game once, I can't pay a second time without reloading.
I like the game a lot, good music and theme. But even on Nooblet the waves of ships come too fast.
To ThisGuyJay: I also struggled with getting 1500 kills on extreme, but now I can do it. Build a rocket and two cannons together, max out their damage (nuke combo). Build three bigdamage nearby. Build two tazers and max them out before the nuke. Build a second nuke nearby the three bigdamage. Have fun.
Showdown is too hard. The bosses have 10,000 Hp on all levels. Why not adjust it per difficulty e.g. easy = 1,000 Hp, normal 3,000 Hp, hard 5,000 Hp, and insane 10,000 Hp.