Anyone giving this more than 3 stars simply didn't play the game through.
The first level, and maybe the second? ok, the second too, those both levels are good to play. 3rd level onward showed up the game's flaws, which are quite serious:
1- CROSSBOW CAN'T KILL SH*T! Upgraded it above level 17 - still can't kill most ships before they leave the damn screen, and yes, after they fill said screen with bullets. The ones it can actually kill PRESENT NO HARM WHATSOEVER and I could only be hit by these scrubs if I steered the lil' vamp on them myself. Enemy HP seem to scale much faster than player capacity.
A most notable example of how shitty is the crossbow: Go back to level 1 and try to kill those lateral laser ships.
2- LESSER SPECIALS CAN'T KILL SH*T EITHER! Actually, SOMETIMES they do, but only when used multiple times, which depletes Special Bar quite fast. Most of the time they are only useful to try to clean the screen a bit. They only cause noticeable damage against bosses.
3- THE BIG SPECIAL IS EXCELLENT AT 3 AND THE MAIN MECHANIC ON 4-5 - That's it. After some time, you just forget whatever the game is about (as a top down shooter) and just go for the "S" and "Smax" bonuses to accumulate enough power to blast the spacebar and kill the lots and lots of ships that you cannot possibly kill in any other way than this OR the punching "damage" powerup, which allows to 1-shot everything but is very luck dependant
4- POWER UP IMBALANCE - The speed powerup is utterly useless. Damage is a sure fire to kill everything before it dissipates and you get flooded again. "S" and "Smax" also dominate because they allow the "press spacebar to win... momentarily" move, which is the only way to progress on later levels.
Suggestion? So obvious: Just fix all that. You have a good idea, story and art.