This looks like it will be a very fun game! Now for the detailed review:
Let's start off with the graphics, they all look amazing! The pixel art is very nicely made. The music is also really good, though I hope there's a lot more in the full version. The gameplay is nice, and the world design is really good. The fact that you guys fit multiple side quests into a very short demo, is really cool, and it even supports multiple languages!
Now, for the things I didn't like as much:
The story is pretty generic, which I, personally don't mind, but others might want some more story development. I wasn't a big fan of the difficulty, seeing as how most of my deaths were just from trying to kill enemies, but it's not a terrible difficulty and maybe it will be improved in the full version.
A few annoyances you might want to fix:
1: When you die in the green water/acid, a human skull rises. The effect is cool, but maybe it would look better as a dog skull.
2: You have to watch the boss cutscene every time you die.
3: A weird glitch occured once when I was fighting the boss, I couldn't move at all, so I got crushed.
There's my over-detailed review! I hope you can take this information to improve your game.