The game-play and the concept is pretty nice and simple,
shoot stuff, collect coins, more stuff appears, shoot more stuff.
Collect too much coins in a limited time and you are screwed.

The sound overall is pretty nice too, but probably can be slightly better.

The only downsides I can state is due to its repetitiveness, but that is kind of expected out of this game, and it would be countered once you implement the leader-board.

Also, some scenarios are rather difficult to avoid:
Ex. A coin at the wall, collect it and suddenly a green guy spawns in front of you there and you died.

I dig it. Super smooth, very responsive. I really like the visual style with this one.

The main menu music is great and fits perfectly.

And you found that sweet spot with screen shake that looks clean without pissing me off, so thanks for that!

I managed to get to tier 3 with 16 collected. I'll be sure to come back though!