Really nice game. Really liked the particles and the slower movement made it kinda tense when the aliens were coming at me from all angles lol.
I'm not sure how I feel about the aliens being able to sneak in through the middle of my bullet columns though. I think making the game faster paced might be good as there is a lot of downtime while waiting for enemies to appear and to get past the first few levels.
Honestly a really nice game, especially for a first one. Some nice gameplay, but the main thing that I think could be better is to decrease the downtime between waves / increase the pacing of the game. Really cool!