I'm not really into auto-survivor games, so don't take my criticisms to close to heart.
I think it looks good, the sprite art is basic but looks sharp. There's a good amount of "juice" in there that helps a lot. I would like to use WASD instead of arrow keys. I think the turret upgrades you get need to be a bit more significant, I didn't really notice any improvements. Some music would also be nice.
I did not play a ton of it, but what I did play seemed alright. Keep at it.