I was only really close to death < lvl 4, until I used that monsters/items are respawned when you enter and leave a lvl (no time lapse) to get "easy" monsters to kill rather than harder ones.
then the next closest would be when I fought the sandworm queen (took me down to 67 health) and then the greater mummy lord (down to 88 health).
then once things started to be non-hostile it was easier (orc pride was always non-hostile, tol falas was only hostile after I killed the master, except for the first level.)
damage output, hmmm, I think I was around 175 (ringil, lvl 10 sword mastery, and 43??? strength I think)
the spider caverns could easily become more difficult (web is annoying), webs in combination with spiders that poison/actually damage you (I was a skeleton so muahahahaha) might present more of a challenge if I played something different.
mines of moria was annoying since it was so large, but it just took more time, not that difficult, but then again, orc pride was non-hostile, so I never got to see some of the new monsters fight me (not going to mention them just in case, this is general discussion after all). same thing goes for the bosses, though it was strange seeing the destroyer have less hp than uruk
that said, what mainly feels broken is that damage output is so much higher than you can raise your armor, so even if armor is maxxed even an iron weapon can still do damage to you. and since monsters generally dont have that high of an armor, they die fast. The main problem here is to find the right balance of weapon damage and armor, and not ruin the game significantly at the start.
Also maybe consider adding a lvl requirement for weapons, yes strength is good and all, but really, at lvl 14-18 you are going to be able to wear a mithril weapon with what you find in the game, unless you get unlucky or spread out your stats. this makes the game much easier, because unlike t2 there are much less encounters that can kill you when you get mithril, so your overstepping bounds is not that penalized.
Also maybe consider making mages smarter, right now they will chase you down black corridors only to be ambushed walking around a corner... make them stay or move to get a better LOS of what is down the corridor. or make them smart regarding light sources or something.
also make it so that you can target anywhere in your LOS by selecting it, right now there are strange spots that you have to shift-target to, and some that you cant even do that with, but you can still see the monster.
and running still messes with LOS in some places, causing you to see what you cant really see.
and also I would change up how ball "spells" cast into darkness work, right now the projectile "guesser" (the green area showing what the ball "spell" will affect) stops when it hits a dark square. maybe instead make it assume all black squares are empty (unless you have explored there), and then it only really checks when you fire.