This game is is great. Level 20 is not impossible :) my advice is to get all upgrades from the legendary shop and get the ion wave (wave rare weapon + tetra weapon will give triple wave, upgrade special weapons in legendary shop). With 24 slots you can make your ship very powerful and the ion wave goes through enemies, so you do not have so much trouble with the ships the final boss does spawn.
Bah, this is HARD! I can usually multi-task pretty well but you really need to split your concentration unto different parts. That is really hardcore! Add badges :-)
Can all the nubcakes stop crying?
The game is well balanced, if you think this game is crap give it more than 5 minutes so you actually know the different skills you can equip. The badges don't take ages to get, only the hard badge takes a bit long.