Ok i just did lower end quest on reaper mode 10 skull Lord of Dust. What i can see, mobs seem to have same amount of hp but take much less dmg, because players are greatly debuffed. First thought was - healing is extremely difficult that make temporary hitpoints even more important in fights between encounters (read wlk and/or affirmation). So what i expect - slower runs with more distance pulling, more unavoidable CC, more instakills. Traps are deadly again - that is nice, some random traps in old quests will make it even more difficult, if it possible to implement. Mobs hit too hard - I never liked it, i'd rather have them hit less hard but little faster, making combat more dynamic, give mobs some sort of alacrity. I see some "carnage" mobs spawning randomly - its nice, they could spawn closer to party/behind/right near player, but give them slow initial attack so its scary and deadly but you have time to react.
I have mixed feelings about instakills - this make good DC caster too strong in a way. Same goes for shiradi, nerve venom will be too strong cc in this setup careful work with DC needed. Player debuffs dont seem to extend on charmed mobs - so they die/kill (did not had time to watch closely) other enemies very fast - that could be concern with charmers/confuse users. Over all i feel this strongly promote balanced grouping: DPS, CC, Traps, maybe stealth runs (healing? if it not gonna be one hit - one shot). I feel ranged/kiters and instakillers will hold strong if there is no way to work around it - maybe give random mobs teleport or something. Obviously some quests will be easier to run and some harder or near impossible - that is ok. From what i see now with rgiht people and some tactics - most of the quests can be done. Soloing quests seems pretty hard, and some builds will do much better than other - but, hey, i dont care.
Thanks for reading and working on this mode.