I'm not really a fan of run'n'gun types of games, but this one could have been much better. Though most should be self-explanatory, a better introduction would have helped. Heck, simply telling the player where to upgrade skills would be okay as I was wondering. (Why mention a need to upgrade things and then not mention where I can upgrade?)
The gameplay wasn't polished. There were lags, but that could just be my computer. The movement seemed clunky and for this type of game, it shouldn't be. Plus, coins often fell onto spikes or magically were glitched into a wall where I could not go to.
As mentioned before, the upgrades were lacking. Frankly, if they had been good, I would have kept playing to improve my character and make the game just that little bit less frustrating. But, not only was it annoying to have to go back and forth collecting loads of coins, but my upgrades didn't even seem to do anything. I got the first shield upgrade and didn't see a difference. Then I got the next one and still nothing. I was shot for the same amount of health and had no extra health. I believe the damage upgrade did work, however, so it could just be that particular one, which is an important at that.
There were also some strange enemy placement, wherein it was hard not to get hit.
I couldn't do any better myself, but I expected more. It seems thrown together and can certainly be improved. And heck, man, just looking at your other projects you've had some great games, so I know you can do better. Good luck with future projects. Sorry if I sounded rude. This game is a tad hard to enjoy, for me at least.