Game controls really tightly and is challenging! It's not terribly complicated but I did really appreciate the strategy of getting used to swapping out in between the characters to reload the other when they are inactive, encourages active attention to the ammo gauges even when enemies are not around (Sitting around with a half empty gauge is no good when it could be reloading!)
I tried a few times and couldn't get to the "end" and I don't know if there even is one. Maybe there could be some kind of tracker for how many spaceship parts you've collected and how much further before the end? That is assuming it isn't an endless wave of course.