Watched this on stream as you know, giving it a spin today. Gotten to level 10 for now, got some initial thoughts. The core gameplay system here works, it is fun, but I think it needs a little more flair. Once you reach a level save point, introduce some sort of choice for an ability unlock, make the player able to create "builds".
Abilities such as: double healing, more damage, survive one death, traps heal you, break rockdoors etc. These are abilities that depend on what is in the game now, I think you can add a lot more.
Gambling/party feel I think would be good. Special blocks with slots or fantasy roulettes giving gold, exp, damage or something else.
Every tenth level, introduce a boss sequence, the rune thing is cool. Some kind of clicking minigame to solve a boss, possibly targeting body parts in a correct order or something like that, using the core mechanic.
Introduce a shop here and there too where gold can be used, also use max gold as score.
Implied randomized story encounters would be cool too. Nothing too advanced, a rare princess encounter, dragon enemy, mimic chest, mysterious crystal etc.
Chests with loot. Loot could just be collectible unlocks.
Edit: Collecting collectable "loot" also provides further investment to play the game more.