I was somewhat surprised by a recent post by LostTemplar on angband.oook.cz:
When I played UN it seemed to me that it is too hard in the beginning and way too easy in late game.This has to be fixed immediately. I can't have players calling Unangband easy...
A big part of the problem, as Mr Templar points out, is that high level Unangband players end up with an obscene amount of hit points. This is a result of making the size stat determine hit dice, which means even a mage can have a large hit dice. I've tried to balance this by having size penalize agility if your size exceeds your strength, but since every item which adds size also adds the same amount of strength, it is easy to ignore this limitation.
If I remove the size = hit dice benefit, there is little incentive to have a high size, and the size bonus feels about right for most of the game. It's only at high levels (and high stats) where the bonuses becomes obscene.
Which leads me to conclude that I should reduce the level cap for Unangband from 50. This way, the per level bonuses for hit points can remain significant as size and constitution increase, while not having to worry so much about the results at the top end.
I'm immediately attracted to the idea of limiting player advancement to level 40. The reason is that almost all mage spells are under level 40, so I won't have to redesign to many spells to fit the lower level limit. In fact, I shouldn't have to design any*, because spell specialists can cast spells 20% higher than their level, so that they can effectively cast up to level 48 spells. Given I have a to do item to add higher levels spells which only specialists can cast, dropping the level limit to 40 is an automatic win for this reason. This should start to address some of Templar's concerns about imbalanced spells as well.
There are two downsides to this approach: tradition, and level advancement as carrot. Tradition means that long time Angband and Unangband players will wonder what is going on when they get to level 40 and no higher - which will mean that I'll get pestered with questions. Level advancement as carrot means that there'll be less short term goals available to higher level players which they can grind towards. I'm unsure whether this is a good or bad thing.
An alternative is to play with the way that hit points advance. I've done this for other stat advancement: in particular the number of spells learned by low intelligence players is capped before they get to maximum level. I could take this approach. It's very much in the spirit of AD&D second edition where you no longer got to roll hit dice after a certain level. Size contributing hit points up only until level 20 would be one such example. This would make extra size add extra hit points, but not too many extra hit points - +20 hit points per increase in size above 18/110. Constitution by way of contrast gives +50 hit points per +1 CON at level 50 for similarly high constitutions.
* Except Fireball III which is level 49.