I don't know much about setting up games in browsers, but for whatever reason it ended up very small in my browser (chrome, on windows, with a 1377x768 resolution screen). As a result, the detailed textures didn't look very good and the text was hard to read. The actual gameplay wasn't affected though.

I think next time you make a game, it'd be a good idea to consider how much content you have in relation to how long you make the game. This game appears to be just dodging arrows at the same rate and of the same type for quite some time without variation. The dodging itself is fine, but it's not interesting for as long as it takes to win. This is made worse by the scrolling background being the same the entire time. As such, I think it would've been better to keep the game a little shorter to compensate the lack of time to make more variation. Similarly, if you decide to do any updates to this later, I think even so much as allowing there to be 2 arrows shot at once later on would improve the game.

I couldn't take care of Heart Boy :(