Since this is a prototype I will assume the feedback you are looking for is the following:
Is the core gameplay loop fun?
What are core mechanics that the player might find more engaging?
Is it easily accessible?
I don't know for sure if these are the questions you are asking/wanting feedback on, but since there is no direction (here or on the reddit post) it is what I will assume.
To answer the first question, is the core gameplay loop fun?
I would say it has the potential to be, although I worry about your features planned on the itch page. I think there is a LOT of polishing that this game will need to go through before there are 20 classes in the game. However, I do think there is potential for each dungeon a player heads towards to have more enemy's geared to a certain stat/weakness that players need to learn and prepare for. There is some real potential for strategy which I like. However the current impact with stats means nothing to me because it isn't established yet. Hell, I think I only saw one enemy. Which is fine for a proof of concept/prototype, but I am still going to point it out.
I will rip the bandaid off and tell you right now that the dungeons aren't fun. They are boring. As I said before, there is basically only one enemy and I don't think there is any music in the game. With a blank background and no strategical element when party building, it is a bowl of nothing. A lot of my criticisms are nice because this is a proof of concept/prototype and I don't bother mentioning most things because of it. However I really worry where the devs priorities lie when in their planned features they don't mention polishing this stuff.
Second question, what are core mechanics that the player might find more engaging?
Well, I definitely think there should be more strategy involved, it's basically all my fun from an autobattler lol. You say that there will be more story implement, so maybe collecting story characters that get fleshed out later could be something? Also there should most definitely be a shop so we can sell our extra weapons/armor that we get in dungeons.
Last question, is it easily accessible?
Yes. UI is fine for a prototype.
If you want my genuine advice, you need to focus on the basics and make what you have CURRENTLY more fleshed out. Working on the story if you plan one is fine and dandy, but don't focus on adding more, more, and more when what you have right now is half baked (which is expected for a proof of concept/prototype).
I don't really write reviews for prototypes/proof of concepts like this (I mostly do playtests that have a generic level of polish at the very least). But I thought I would get out of my comfort zone and give it a shot. Let me know if you have any questions dev.