Alright because this was all on one map I presumed it'd be quite short so I decided to bump it up to the top of my list of games to try and gave it a go.
I started playing this yesterday and finished it today.
Overall, I really enjoyed it. In my opinion you mostly used the mechanics you choice very well and it's quite amazing what you were able to do with so little.
I choice Knight, Sorcerer and Dancer on my play-through. I really really like how you planned out the classs here in the description, though it would've been good to describe them in the game too before picking them if that were possible.
Mapping was very nice, I felt everything was about the right distance and visually appealing, very enjoyable map to roam through. Music was also good, it felt mostly cheerful and so did the facesets and sprites you were using, so they both combined well together.
I felt you balanced the whole game really well. You couldn't easily with battles for the dungeon your underleveled, and at the right levels the game provide a bit of a challenge.
The only two parts I got stuck on was the Earth Spirit and the Dark Lord final boss, I talk in a little more depth about the final boss near the end of these comments.
I really liked that you upgraded to better equipment once you got to the dwarf area, and then in that last area you can buy some rings. That made gold more useful throughout the game.
I also thought the Dancer class was quite creative. I liked how you mixed it up instead of having a Healer class.
When choosing the characters though, after entering names for them I had to click enter on my keyboard twice per character to move to the next screen. Not sure if that's a bug or something wrong on my end though. An exit game option on the title screen would've been nice too.
Flash on the Hero also dealt very little damage so I never used it. I think even when those certain events that changes the Hero happen it still dealt hardly any damage. Also the final weapon, I think, was less powerful than other weapons. It may have been better to give it slightly more than equal stats to the dwarf sword?
I also felt the defence skills the Knight had were mostly not that useful against most of the game enemies, but it was still useful to use them with Shield Bash and that was good though.
You also have one bugged skill on the Hero, Revive didn't work on other party members, it just healed the Hero some more HP.
I also didn't like the Hero starting a level 1 again at the point Hero changes, but I quickly accepted it when I realize the character had much stronger stats.
I thought that plot twist was good, it added to the game experience and took me by surprise.
Nice having the feature to talk to the NPC's as well. I also liked how you unlocked the boat for the dwarf place and the airship.
For a one map game challenge it's pretty impressive all that you were able to do and accomplish.
It took me a LOT longer though to defeat the Dark Lord, I felt it was quite difficult in comparison to nearly everything else in the game.
Overall my game time says 3:14:36, but because I ended with a blank screen it didn't count the final boss, and I reloaded save filed each time I decide in battle so it's probably another 30-40 minutes. I don't think the game crashed, but it just left me with a blanks screen after some extra dialogue? Is that right? I think it would've been better to exit it back to the title screen.
My last point was on the codec, was it meant to do anything? It always get it couldn't connect to the internet, I don't know if there was some internet feature in the game then, but my internet connection was on.
I also don't know if there was a secret ending I missed or not?
But that all sums up my thoughts and comment on the game, good job overall it shows you've put much thought and effort into this and it the end game was fun to play too!
Other than a few bugs and tweaks, which is expected with any game, I don't see much that could improve this as a one map game, so congratulations on that too.
Good luck with your future games!

I do still plan to try out your other finished game sometime in the near future.
I was also wondering, could you let me know where you got the custom graphics from for the facesets and sprites? I quite like them!