Yep, really love the concept and it's quite addictive, but the balancing sucks. Even if you don't make any mistakes at some point the ships become virtually understructible, it becomes more of an avoidance game than a shooter.
I also have the feeling that the damage resistance of the enemies increases. Not only the amount of hitpoints, but also the 'armor' so to speak, but that's just a feeling, I'm not sure.