You could steal a lot of puzzle ideas from Lufia 2: Rise of the sinstrals (snes), and Brainlord (snes)
Sprinkle in a few of those purple loot chests and I think we got something everyone could enjoy
For the combat against baddies you could add a healing potion that players could throw at each other (like that love potion, but for healing) and maybe add a survival element (if you die you gotta wait till the next day)