Played until level 17. I got the quest "Gamble Laser Tier 3 1 times" and do the same for a plasma weapon. This quest is effectively not possible without paying. The ~5 hours I have played so far have gotten me 49E. I would need another ~100E to complete this quest, which would easily take 5+ hours of farming. Or, I could spend ~$0.25. This is one of the craziest examples of a pay-to-win style system I have yet seen. I will certainly no longer play this game.
I really want to like this game. Its an interesting twist on tower defense type games. Its feel is just "off" somehow... It really doesn't feel smooth and engaging. Great try, but a near miss imo.
Running out of upgrades before game ends = lame.
Hitboxes on big planes are kind of annoying.
Spam left clicking shouldn't be able to indefinitely stall any enemy.