Honestly this game is a gem and is doing a lot of interesting things. The preview for the new layers looks very good too.
The biggest off putting thing to me when initially trying to learn the game was just identifying what items did - that being tied to intelligence is a bit wonky. An experienced player is going to know what items are just based on the sprite and or just know a series of crafting goals to build intelligence; whereas a new player is the one that needs this information the most but its withheld from them (or they just alt tab to wiki dive). Its also a bit weird in the aspect of: Great I crafted a flashlight - oh I suddenly know exactly what this serum does to me now. I think it would be a lot better if identifying items and their qualities was tied to just brain integrity (or tied to both); as in you by default know what at least most items are (not like IC you haven't been regularly doing training), but you still need that intelligence to craft it at all.
Past that, I'm sure you're aware of the QoL mod that does a whole lot of improvements that just the base game should offer. The save system it offers should just be opted out in a hardcore descent or something though.
Finally, there just needs more reason of why you're needing to descend. I'm sure you have plans for this already. Just an idea would be you could have each run with a guaranteed drop that the player knows of before hand or something; e.g. an experimental weapon or something that they're supposed to retrieve (but it still has use to survival).
So keep it up. Really look forward to seeing how this develops.