Unfortunately it uses localized keys instead of the key locations, so `x` and `z´ is very inconvenient on my keyboard setting (being "QWERTZ")...
There should really be an option to at least turn the volume down.
Some feedback on the bosses' health is dearly missing. In my second turn I had some "car chase" thing and got rockets to fire at the enemy. But it didn't seem like they made any damge whatsoever...