Thank you so much for your feedback! it's basically the distinction between cyborg ships and alien ships that determine what you can do. Once you collide with an alien ship, you get the option to place one tower on your ship, if you collide with an alien ship and have no space left for a tower, you lose. Once you collide with a cyborg ship, you can't place another tower, but the towers you already placed will fight against 1 - 2 enemies, just like in plants vs zombies. And as to playing criss crossed - you can change the keybindings in the settings if you wanted :) (I tested / played it on a german QWERTZ keyboard). Sadly I didn't have enough time to implement changing the scale of the window :(.
Anyways, thanks again for the feedback, I really hope you liked it!