Dungeon crawler musings

Over the years I've played many different types of dungeon crawlers and am still on the hunt for that perfect game system to use that allows for GM run games, or randomly generated solo hackathons. I got part way through writing a history of all the crawlers that I've tried and discarded, but you probably don't care about that plotted history of gaming... so what is the point of this post I hear you say?

The point is for some random musings on what I'm looking for in a game to try and solidify things in my mind as the hunt continues. I really don't want to write my own from the ground up as that would require balancing so many things... I've tried in the past and could never get my head around the best approach to some of these things.

1) Solo play/randomness
I don't get to play with a group too often, so one of the important things for me is randomly generated adventures. Not just the layout, but events throughout the story and an actual end goal. The original Warhammer Quest did this well, as does Silver Tower, Shadows of Brimstone and, to some extent, Advanced Heroquest. This part is straight forward to fit into a system. I've been playing with the theory of ripping apart Hammerhal and seeing if the mission levels still work as random layouts and event triggers. More details on this when I finish putting together the figures.

2) Character selection and evolution
I really want the characters (and potentially key villains) to evolve over time in a structured way that makes sense, rather than some of the slightly suspect, abstracted methods used in things like Silver Tower or Hammerhal where characters forget skills between levels... because magic. Random or fixed stat/skill allocations are also a weird thing to imagine. Why, for example, would you suddenly know an archery skill if you're a close combat specialist?

3) Tough, varied adversaries
I like to theme dungeon crawls with adversaries that provide a suitable challenge to the adventurers. Warhammer Quest is really good at this. Others less so as they assume some sort of GM control. Shadows of Brimstone has some level options for the monsters, but can still end up under/over powered quite easily

I've tried to write some bits for points 2 and 3, but I don't really have the time or brainpower to deal with the creation of a whole ruleset. At present I'm trying to work out the best options to investigate further, so any suggestions would be gratefully accepted.