Since this game took quite some of my time, here are my thoughts:
The game itself was quite fun. The levelling up was a bit imbalanced, in that the number of bullets fired actually counted for more damage than the base damage multiplier, which didn't quite make sense to me. Also, the hitbox could have done to be where the mouse pointer / tablet cursor is. Because otherwise, it makes things absolutely confusing.
Otherwise, I finished it, got all the stars, and quite enjoyed myself.
The graphics were alright... I guess? They could have done with a little bit more finesse. For instance, killing a big angler would cause it to break into two small anglers. Even a quick animation or explosion for that would have actually added the effect. There, I really felt just how austere the game was -- I mean, you had an amazing title screen and amazing menus and then, you come to the enemies and think, what the heck? Why didn't the artist put enough time with this?
The music was excellent, but:
1) The looping was awful. There were cuts and noticeable breaks. Surely someone could have done with a 'wrap remainder' option when exporting this stuff...
2) There could have been a bit more variation. I've heard the same level theme over and over and over again. Sure, Adventure Island had that on the NES, but... in some of the stages, the music was actually changed. I think this game could have done with that.
VOICE ACTING / SOUND DESIGN
The sound design was alright, by and large... I guess there needed to be a bit more variety with the enemy death sounds.
The voice acting, on the other hand, was awful. Our Adventure Island hero had times where he sounded like an 18-year-old and an 8-year-old within the spam of 5 seconds, partly because he had dialogue and attack sounds going together within close proximity of each other. Also, all the bosses sounded almost the same in the way of voice. I know this is a cliché storyline, but the voice acting didn't need to add to the cliché by a hundredfold.
And speaking further on awful voice acting: the hurt sound actually does not play when you're in a dialogue sequence with a boss. If anything, you should pause until the hero and the boss have both finished speaking, AND THEN start firing the bullets. The hurt sound is often a way for me to start being aware of my surroundings, and without it, it makes the game confusing.