Quite pleasant music design, good graphics, overall enjoyable game with decent controls, not a bad boss battle. I loved the coin-explosion animation for the chest and the large number of coins compared to the bushes I chopped down (I always felt like Zelda had too few: If I'm chopping bushes to earn money, gimme more faster!).
I am not usually one to complain about open-ended level/area design, but that is the area I would most recommend that you focus on. First, you have to go through half a dozen screens with zero content and no branching, just to get to the cave; I'd suggest the cave be on the first screen there, or perhaps the second (so you'll likely have grabbed the sword). If you want some distance when the character returns to that spot, there are other ways to achieve it. (The cave itself was not a bad design, if a little back-tracky.)
Secondly, the town wanted me to go to the inn, but, being a Spade, I wandered. And I found just a ton of open areas with no dangers (which was actually nice), but also no content. I could basically get hints about upcoming areas to explore after the storm (lighthouse, graveyard, mayor's house, random buildings), and coins from chopping bushes, but that was it. Several screens had me stuck in a tiny spot where I could see the screen but not interact with it unless I backtracked and found a way to it -- which would be fine as a preview of "aha, the boss/treasure is over there" but this happened to "preview" spots I was at just two screens ago. One "previewed" a corner of the island next to otherwise all ocean.
(I couldn't tell if I couldn't enter the houses or just hadn't figured out the correct button. Having the doors react to "knocking" in some fashion would be useful.)
Earthbound has the police cordon off the not-useful places at the start, so you can only really go up to where you're meant to go to progress the story. This was funny, but also useful to prevent the player from spending time in ways that have no long-term effect on the game. I recall A Link to the Past being pretty restrictive at the start, in a natural fashion by not letting you chop bushes yet (or bypass guards?).
You can have some larger open areas, but, in general, think of areas as having enter/exit points, and design the screen around that concept. Trees and rocks and cliffs and the like help guide the player toward useful content, much like lit-up areas ("go here") and broken cars, fences, and trash piles ("you can't go that way") do in Left 4 Dead. If you do it right, the player doesn't even notice that they're being led around; they feel free to do things, but also are physically prevented from wandering too far off course.
(World of Warcraft did this between low-level and high-level areas, not as a hard limit but some pretty obvious signs that a certain area is Bad News. That I ignored those signs and got my level-12 character killed by a level-40 spider is my own fault. But most games won't even let the low-level characters get anywhere near the high-level stuff unless the player has been particularly tenacious in bypassing the signs.)
Anyway, that's the area that I think could use the most improvement. The only other issue that I ran into was a minor fine-tuning thing: It'd be nice if bumping into the wall slightly off from the path just bumped me down toward the path instead of being a hard stop, so that it felt easier to get my character in where I wanted to go. That's not likely a big concern at this level, but it's something to consider for smoother controls once you get to bigger projects.
This was a pretty good game! I might play more of it later (I'm just kinda dipping my toes in the water for a few of the games I just got, and offering feedback if the game is good enough to warrant a little polish). Thanks for making it!