The new formula is: (xlevel + Con)% chance of regenerating 1 hp
each turn.
This formula has been extensively playtested throughout the whole
game (including two ascensions). The intention is to make late-
game combat more interesting: early game the HP regeneration rate
is potentially slightly faster but not significantly changed, but
in the midgame and lategame is substantially slower because there
is no longer a big regeneration boost once the character's xlevel
is in the double digits.
With the new formula, I'm finding that my characters have to heal
with potions (rather than by waiting) in places that they never
had to before (e.g. lower Dungeons, and upper Gehennom), which in
turn means that fighting efficiently is now more important than it
was before. (In fact, in one of the games I wished for potions of
full healing on Astral for safety, although I think I would still
have won without.) It's also generally the case that you can no
longer regenerate "mid-fight": you need to disengage in order to
heal up. This made the game more fun as it meant that escape items
became more relevant, and I was using a greater range of items
throughout the game than I normally would.
The ring of regeneration has also been slightly buffed: it now
heals an extra 1hp per turn unconditionally (rather than becoming
less effective as the character levels). In both my test
ascensions, I found a ring of regeneration, but intentionally
refrained from using it in order to ensure that the new HP
regeneration rate would be tolerable even without one.