After playing through the Xpac content in all three difficulties on four different characters now, i felt the desire to give some feedback.
My characters were a 2H ranged Vindicator, built around Savagery and Storm Spread (sc), a beefy 2H Ritualist (sc), vitalitybased, also using Savagery (+ Feral Hunger and Necrotic edge), an even beefier Stun Jacks Purifier in hc, and a very fragile BwC-Sorceress (sc). I started from scratch with a fresh installation of the game, and my characters are quite undergeared still.
First and foremost i love the expansion and i think that it is a fantastic addition to the game. The visual design and the lore are better than anything else in the genre imo, but what really mesmerizes me as an aRPG addict are the new items and components wich open up countless build possibilities. (I still miss soooo many blueprints… 
:D.). And i love Gloomwald and Ugdenborg and all the new factions, both from a gameplay perspective as well as from a loreoriented perspective (if that is an understandable way to phrase it). Oh, btw - can i marry Korinia plz? :D.
Please forgive me, that i will criticise a few things now. It’s because i love the game and want it to be as good as possible.
The one thing i dislike about the expansion without having much hope, that it actually can be improved, is the layout of Malmouth as a combat map. The leveldesign, so to speak. There simply is too little space imo, the paths are too narrow with too many stairs and too many obstacles cluttering the combat field. In conjuction with the high mob density and speed this renders the typical advantages of mobile ranged builds useless. You simply have to be very tanky in Malmouth, there is no chance to manually dodge most of the incoming damage. On top of that the stairs sometimes seem to be to narrow for the game’s pathfinding system to work properly. Often my charcters dance around the first step of the stairs for a little while, before they finally start to climb them. This adds quite a bit of tediousness to the gameplay.
I understand that Malmouth is intended to be a zestful contrast to Ugdenborg, but imo in it’s current state it has to big of an impact on the playstyle.
Other than that the general difficultyceiling and some boss encounters seem a bit overtuned to me. A lot has already been said about this on these forums, and i’m certain this issue will be adressed in future patches.
Just a quick summary: To me the xpac seemed too hard on Veteran, no matter the build or state of gear, but mostly fine on Elite and Ultimate, where only specific encounters gave me too much trouble. The poisoncrab (carraxus?) and the aethercrab in the mines near barrowholm hit a bit (not much) too hard imo, and the Aether-Log (shaper of flesh?) fight could use a little love.
Against Aether-Log the only strategy that has worked for me so far, is to run behind him as fast as possible and to dps him down quickly. (FeelsPoEMan.) If i actually engage with the adds and try to dodge the aetherbarrage, i usually wake up in town scratching my head :D. I only did this fight on Veteran and Elite so far, so i have no clue, if the cheesy run-behind-him strategy still works in Ultimate. I didn’t have more than 86% aetherres on any character, but i didn’t go in with less than 80% either, and i tried to overcap and used potions to counter possible debuffs. The second and third phase are laughably easy in comparison on Vet and Elite. (This of course might be very different in Ultimate.)
I didn’t try to engage with the new nemesis bosses so far (my gear is too bad still). As a professed coward i would be happy, if it would actually be a tad easier to run away from Super-Papa :D. He’s really lightningfast and to get rid of him is not so simple.
Well, i guess that was it. Despite all my criticism i enjoy the game a lot and hope that Crate sells enough copies to consider yet another Xpac.
Thx for reading!