Fun game overall! I enjoyed the variety of stages you had and the enemy path finding seemed to work great (that's something I always struggle with). The particle fx was really nice, especially when bullets impacted the walls.
If you wanted to improve some, I suggest upping the difficulty some. I never really felt threatened by the enemies in the game, I could either breeze past them or destroy them quickly enough to not have any issues. A simple difficulty option that increases damage from enemies and player damage would be a simple fix that could add a lot of replay value.
Overall, quality and fun game!