Add autofire, or an option to upgrade shooting speed, because clicking rapidly is way faster than holding fire. A progress bar on upgrades would also be nice, and an option to leave between levels either to the main menu or to level select screen, because now i have to start next level and leave from there. And lastly an upgrade of the movementspeed. Otherwise a good game.
 "Fortress Magnus"){kind=icon}
 "Impasse"){kind=icon}
 "Pogo Rampage"){kind=icon}