Your game is frequently challenging for the wrong reasons. Block you can eat can still shoot you at point-blank range, resulting in the occasional kill that would have been prevented if I had waited another half second, except in situations where speed is important to survival. Also, find a way to show players that the triangle lines of death can disappear. It makes the one with the large triangle and circle actually possible (14 I think).
Next, your difficulty scaling needs some major work. Level 15 was easily one of the hardest levels in the game due to how it mixes nearly every enemy type in the game, yet it was just over 1/3rd of the way through the game.
Next, 21 and 22 are in completely different leagues with each other. The homing shots that only disappear with the blocks are so much harder than the white straight-line shots that making this level the next one simply doesn't work. You would have to put a limit on the number of green shots in some way for this level to work at all with your scaling, or at least make it so the shots are null once they leave the screen so we don't get killed by an unseen bullet. No player likes a kill they can't see coming. And even with your current scaling, 24 and 25 should be switched.
One of my greatest fears playing this game is that you would make a reasonable white-shot level and then immediately follow it up with green-shot in a similar layout. Upgrading from white to green is a World 1 to World 2 upgrade, not a level 1 to level 2 upgrade.
Your game is okay, but no one will finish it outside of those with mobile mice and determination. Honestly I stopped having that much fun with this game about halfway through this review, and I started it with level 15. It doesn't help that green shot eventually floods the field, and at that point my hurtbox is so large that sometimes I can't even avoid them coming.
The last level is a gimme level, and the only challenge in 39 is making sure to keep track of how far your square will grow with each feeder block, for anyone curious how this game ends.