First some general non-monster comments on features/bugs:
Running made me walk into a visible summoning trap before stopping.
I can't figure out the effect of the priest spell Smite Evil. Is it supposed to increase damage? Does it override potentially more powerful slays? I switched on the numbers, but couldn't tell.

I found a few corridors ending in dead ends. This seems new. Not a problem, but wanted to check whether it is intended.
There seems to be a problem with light intensity. My randart lights (+3 light intensity) only gave a 2 light radius, unless I equipped another +1 light, in which case I got a 3 light radius.
Now on to monsters (this is very subjective):
A 9-headed hydra trampled a gorgon. Feels morally wrong.
Trees are currently classed as insects in monster knowledge. This is the wrong kingdom, let alone the wrong class or order. It's like classifying balrogs as a kind of slime mold...

I like the changes to the following monsters (or monster names): Atlas & co, dark elves, Maias, "Trees", troll scavenger.
Thematically, the trees ought to be shallower in the dungeon. Maybe down to 1800'? They shouldn't really be there on balrog depths.
I don't particularly like the following names: Dunadan of Angmar, southron assassin/archer, crow of Durthang. They seem unnatural and simply to be forcing Tolkien place names in. I wouldn't mind as much if the place names appeared in the monster descriptions instead. I actually have the same issue with bat of Gorgoroth. The Druadans also feel rather forced.
Feanorian Raider seems to give a bit too much exp. Maybe I shouldn't complain...
Faegweath, Cantoras and Vecna are not hurt by bright light. I think the same might be true for some other high level undead.
Draebor appears to be warmblooded, while imps are not.
Element-breathing ants and electrocuting centipedes: not a big deal, but I think I prefer the old versions. Leave the fire breathing to...
Dragons! Here comes my big gripe. Dragons are supposed to be rough, tough, mean and very scary. Instead, after many years of power inflation, they are pathetic. In the olden days of Moria, young and mature dragons were formidable opponents. Baby dragons weren't in, but, really, these shouldn't be wandering around without their mothers anyway. Ancient dragons were serious. In fact, the monster memory even had a special entry for this one monster type: "Ancient Dragon (Beware)". Ancient Green Dragon - presumably named after the pub in Bywater (...presumably named after the pub in Cambridge...) - was notoriously vicious. And the Ancient Multihued... well... *sigh*... And now, an ancient dragon is weaker than a killer white beetle. Really?
Oh, and Kavlax got stuck in a web.
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