I'd say there are a lot of potentially very good encounters in the game, but again it's a question of devs putting in enough difficulty so that the player can actually experience it
There is one fundamental problem with how increasing difficulty works in PoE, and that's that it leads to longer battles and in the end, to safe rotation routines. The amount of monsters increases, their hp pool (already extra large, in hundreds) increases, and their defences increase to the point that penetrating them requires many abilities, and at the same time, their defences
against decreasing defences increase. Best example is trying to lower fighters' armor with lower resistances spell, which targets fortitude, when their fortitude is at ~120sh levels, which gives debuff err about 0% to 3% chance to land.
Strangely enough I pointed this, what looked an odd design to me, during PoE1 beta (spells that decrease defences often grazing/failing against defences they have to decrease) but it doesn't seem like folk are as confused by this design as I am.
By finely micromanaging abilities and/or exploiting AI (because the AI is
very stupid), you will eventually beat any encounter and outlast the enemy, but the principle will, generally, remain the same on any difficulty, it's your time which will suffer the most. Consumables, yes, maybe, but so far (level 10), I've yet to encounter anything that can't be beaten by same tactics as PoE1.
You find some narrow space, you try and CC/distract with summons the extra PoTD mobs, put as many debuffs on enemy as possible and gang up on a single dude, because they're so tough mano-o-mano and "builds" matter way less (single one-handed weapons with higher penetration preferable here for beginning of the game). And thus you proceed from 2-3skull/redskulls dude after dude until it is over.
IE games difficulty only increased damage you receive, in battles that would increase the gap for a mistake and make you lose more, but they did not waste extra time of yours.
Thankfully you can pace the fighting how you want it, as game lacks the required population levels of lion prides to make you literally go mad. Otherwise, I can easily see maximum difficulty, well, just becoming tedious quickly. At least fighting just human armored dudes for me already became tedious after (insert number) valera 3 skull halbedier with autoheals/x pirate pistoleers teleporting around for AI lulz.