Most character advancement systems are really stupid, take Fallout 1/2 per exemple... Great games, yet you are going nowhere without a smart character.
A stupid brute getting destroyed in melee by a weak smartass the same level ?
Or being at level 15 a great doctor/scientist without ever using/seing the skill in use.
I don't like it when a game tells me that i will never be able to cast a spell because i'm a warrior, or doesn't let me use that maul to crush that rat cause i'm a mage, thus too weak to use it correctly... Bla bla bla. Yet i'm strong enought to put that maul in my backpack. Mhhh logic.
No what i'd like to see in a roguelike when it comes to character advancement is :
* Starting stats that matter : not ending the game with everything maxed. A weak guy *will* probably develop some muscles (even if only from carrying/lifting what he finds in the dungeon), he won't end up arm-wrestling with Hulk.
* No restritive classes... Using a background at start of a game would be good enought to determine what your character is allready good with, adventurers have a life too before going into the dungeon right ?
* Skills and abilities, loads of them, organized into Skill-Trees
* The costs of upgrading skills, abilities should be based on starting stats and background (if present in game), the basics of skills would need to be learned by use. Exemple : after bashing enought rats, our character learns the basics of using melee weapons. Other exemple : our adventurer is under attack from Orcs armed with crossbows, eventually he will learn from it how to use one.
* Experience system based on learning new things : monsters will not give xp forever.
* Experience should only be able to be spend as certain momments : before sleep or when getting down a level per exemple, hoarding xp in Sil pe in case there is a forge is not such a good mechanich imo. Great game otherwise.
Now if only i could code better.