Just tried it on my tablet, my thoughs:
The html5 demo is inside a really small rectangle, if it took the entire browser view and so the touch controls were not easy to use, it might help with at least having a fullscreen button, or just having the game using the full window by default (letterbox integer scaling is used?)
I know there is an apk version, but the demo being lighter without the wrapper, some people may prefer playing the demo inside their browser rather than downloading the package.
The apk uses cocoonJS (spotted it when I saw all the needed permissions, I think there are ways to reduce them, but I am not a cocoonJS expert), and so with my samsung device, my user experience will be affected, in brief, that is what I saw:
The fireballs are kind of hard to hit ennemies with, as they are small, but maybe with more experience during gameplay I will improve.
The advertisement at the beginning of the game is working, however, there was no background on the title screen in the apk version (it was dark grey it seems)
The collisions between the character and the blocks can be weird at times (I suggest having a platform rectangular sprite, with the animations of the character pinned on it, since the platform behavior works best with that)
The framerate of the game was not that great on the apk version, but the web version was smooth inside chrome for android (this is where the fact I am using a galaxy tab 3 10.1" may play a role, as I heard that cocoonJS had issues with them)
In the second level, you can be killed by the ennemy near the exit when the level is finished.
I saw little seams on the ground, and, on the web version this time, It seems I could not shoot anymore after getting the crate with spikes
Apart from those issues, the game is nice, and the issues are actually pretty basics so you should be able to overcome them.