Already a nice game! Here is my feedback:
In the first level, the player walks beneath that hallway roof. I don’t mind that much that you don’t see the hero for a short while, but it would be nice if you could see the hero right before he walks into the castle.
In the castle, you should add a portal/door at the entrance. This way you could walk back to the previous level, but also let the hero start on that entrance instead of in the middle of the castle (you can select a target door just as you specify a target level). The rest of the levels also suffer from this same issue.
Since I currently don’t support doors bigger than 1 tile (sorry about that), maybe it’s better to guide the hero to that 1 tile portal. I have to see what I can do to make doors bigger…
Also there are 2 kinds of doors:
1. A real door, where the player needs to walk up into it
2. A portal, where the player needs to walk right on top of it.
In some levels, you should use the portal instead of the door.
But next to these comments, I think your levels look really nice!