I enjoyed seeing Terry's posts about his progress on his 7-day roguelike so I'm writing one too. No promises about keeping this up consistently.
The classic roguelikes I've most played are Nethack and ADOM, so any critical generalisations I make are mostly about these. (The Angband family seems to suffer from most of the same problems without the redeeming features though.)
My 7drl last year was a curated selection of some common elements of roguelikes - tactical combat (focusing on evasion rather than slogs), inventory management (limited to single-use powerups), the identification game. This worked out pretty well, so I started thinking about trying to do something similar but with a different subset of roguelike components. Specifically, it would be nice to include richer character growth. Gaining items in Zaga-33 is a form of growth, but because they're consumed when used their effect is quite short-term (gaining identification knowledge is long-term growth, but very limited).
I'd classify the common forms character growth takes in roguelikes as follows: either intrinsic (innate abilities of the character, usually permanent or close to it) or extrinsic (granted by items which can be lost or replaced), and either interesting (granting new abilities and changing the rules) or boring (making numbers go up).
Advancement in roguelikes often ends up being quite dull because there's not much choice involved. Intrinsic growth often lacks any choice at all (you killed some things and went up a level and now you are stronger). Extrinsic growth often offers obvious choices where one alternative clearly dominates another - particularly when the choices are boring (it's very easy to determine which of two numbers is bigger; take the sword with the most plusses on it). Decisions often come down to either being obvious or a pure gamble once you understand them: either you know fire damage is going to be better because the strongest enemies are made of ice, or it's unknown whether you'll turn out to need one or the other. Worse, most of the time the correct choice is "carry both of them and switch between them as appropriate"; i.e. not a choice at all and just tedious micromanagement. (Apparently Brogue has treasure rooms which only let you take one item; this is good because it removes the "all of the above" option.)
So here I'm trying to create a character advancement system based on choosing between interesting alternatives, in such a way that there's no obvious best choice but without it being a matter of blindly gambling, and committing to them rather than micromanaging.
So far I have four enemy types with different abilities, and they're super-easy to kill because the player has a ranged attack which stuns them. No advancement yet, but that's totally the goal. (Zaga-33's goal was a system of politics based on making and breaking deals with different enemy factions so uh I guess we'll see.)
(You can only see three enemies in this picture. Like I said: abilities!)