Gameplay is solid, although there's a few bits and bobs that could make many things much better:
+ I would recommend that you add a little rest period with a timer (maybe also with a button you could push to start the next wave?), as this could give a player a much needed moment to tweak their ship.
+ Another issue is that when modifying your drone, sometime block selection grabs a block other than the one you clicked on, and if you don't happen to catch this, you might completely disassemble yourself by accident!
+ As a final point, I strongly encourage you to possibly implement some form of random or psudeorandom map generation, this way each run makes players think about their strategy.