A little hard to see the bullets against the background when it's a similar color, but apart from that this was great too. Addicting; easy to replay, with varied foes and rewards... the reward system seemed a little imbalanced too though. Easier to get downgrades than upgrades, so in the end it feels like picking up the mystery crates may not be a benefit after all.
Feel like there might not be a benefit to having downgrades there at all, more so either upgrades or nothing, and so luck could influence progress but not vice versa.
Anyway: overall, great game. Smooth mechanics; fun to play.