Interesting game and pretty fun, but first there are three things that are HIGHLY needed to point out.
First off, HEAVY epilepsy warning. If you are seizure prone, do NOT play this game. There are TONS of flashing lights and bright colors, so take warning and play with caution.
Second of all, this game has PLENTY of "Screen shaking" so if you find yourself getting sick, then that might be the reason why. The screen shakes with explosions and firing your weapon frequently. If you have motion sickness issues, definitely do not play this game.
Third, this game also has a lot of heavy "screen filling" action, so if you're on a low end PC, you're going to have a hard time playing it since the more sprites that appear causes your game to slow down because there are too many sprites on the screen and too many things happening at once. If lag becomes a major issue, it would be advised to stop playing.
Those three things aside, if you CAN play this game with no motion sickness, seizures, and plenty of lag, then this game is pretty neat. It's rather challenging, but it is also quite SHORT. Tons of action, and all in all not too bad of a game. The concept is quite confusing at first, but you get the hang of things eventually. Pretty good upgrades that help you along the way are available, and it's pretty fast paced in nature. All in all a pretty good game, but not one I would play for long periods of time.