Overworld:
Grass area. Open and nice. I would recommend looking to add more detail and variety for the look of this place for future games.
Water area. Was nice.
Snow area. This place had a nice linear path to make it unique on how you play this overworld.
Fire area. The two caves the player goes through this dungeon are amazing. Why? Because it makes something new that the player has to go through. The getting the 3 keys in this area is my favorite part of the game because it makes for doing something not normal. That sign post for getting the keys is great.
Purple area. Straight and forward. Could use variety with what you do on the screens here. Like maybe a lave pit? Burn a torch. Something like that.
Flower area. Loved the bugs and all the flower and the skeleton. I like the skeleton because it tells a story. So telling a story with surroundings is always a good idea. The one text box here is awesome.


Dungeons:
Level 1. Short and simple.
Level 2. I like the overhead bridges and the spinning tiles.
Level 3. Big and open. Has a nice nonlinear approach to the dungeon.
Level 4. Favorite dungeon. I like all the rooms and that it's easy to go fast and I like the usage of the enemies. One thing that is really cool here is the custom tiles that do things. With the spikes and red tiles.
Level 5. Each floor is different which is great.

Bosses. All of the bosses are custom which I love.

Overall: I love the effort clearly put in this quest with all the unique enemies and custom tiles. Keep it up. The dungeons show a lot of promise with all of them being unique and have their own ideas.

This quest is not perfect, but it does show a whole lot of potential! The dungeons (at least for me) were brutal to go through but for the most part very well designed. The graphical work could use some help, as some places look stunning and other places don't look so good.
The final boss was very awesome and I like the idea of playing as bowser. I would prefer more NPC's but I'm just biased. XD I can't wait to see what you have for us next!