Hello! Really nice 2D shooter! I think it needs a little tweaking in balancing and pacing.
On balancing, the beginning is hard to kill anything, but as soon as you get double shot and better shooting rate with power ups it becomes "snowbally". At the end I was firing 5 streams of constant bullets that killed the enemies pretty much the moment they spawned and had so much health that I could take any hits and be above 700 health! lol
Regarding the pacing, I think the rate os spawn should increase more constantly during the game. I felt the spawn rate was much higher at the end, but even than it took a while to get to the 150 enemies killed.
Overall, this was a great and fun game! I loved the graphics and the sfx was cool!
Keep up the great work!