Cool game!
First two bugs: The 'return to hub' button is brocken, so I had to close the game every time and restart. Secondly as I restart the game, maybe one of four times the dialog was brocken (wrong letters in the wrong place) and I could't continue and also have to restart the game. I don't know if its your bug or just really strange behavior, but you should test a few times an see if any error occurs (maybe in a devolopment build where a console pops up if there is any error).
But after all it is a very nice game, all the mechanics are working and also feel good. The only funny thing is that level 2 is much harder then 3. In my opinion because in level 3 you already know the shooting and can better dodge + there are waves without shooting creatures who are easier. And maybe there should be a health pack or something like this as there is no way to recover life.
If there was a ending after level 3 and you fix the bug, let me know I would love to see it!