I'll critique this a little stronger since you're selling it for money.
I like the plot, the "real avatar in a real videogame" idea is a new twist on an overused idea.
The details were great like edge assist for walking around corners, optional hints, and ambient noises.
The level design was very intuitive for teaching the game mechanics, but there was still pointless text onscreen telling me generic stuff like "complete the level". Too much pointless dialogue too. Efficient and concise is the only model you should abide by when it comes to video game text.
Good soundtrack, a bit of cavestory vibe.
The load times were kinda long and often, which is pretty bad for a 2d pixel web game with not much content between load times. I'm sure the final game will have be all downloaded though so that won't be a problem.
I liked all the textures but noticed a small number of pixel density inconsistencies (like the pause overlay before the crab battle).
Also glitches: when dead health goes into the negatives, and some attacks should get blocked but aren't shielded.
Verdict: Worth $15? Yes. Will I play the final game? No, I personally want more mechanical depth and higher skill ceiling if I'm going to spend time on something.