The Last Sarkorians DLC turned out to be fully integrated into the main campaign. It adds a new class (which is sort of a mix between Druid and Fighter, sacrificing spellcasting for a focus on Wildshape) and a new romanceable companion with a full set of sidequests taking place in a new multi-part location.
The companion is decent enough if you spec him toward Charge damage, though he’ll need quite a bit of buffing support. The sidequests meanwhile don’t feel out of place but are a bit unbalanced in some places. Like, why does that Bloodrager have DL37 Cleric/Wizard buffs on him? As long as you’re geared to handle swarms though (and the companion comes specifically with an anti-swarm necklace, with more available in the new area) for the most part the added content doesn’t feel unfair or forced. And more importantly, clearing it won’t unbalance the main campaign’s progression.
Something that cannot be said for the integrated version of The Treasure of the Midnight Isles DLC. That one is not balanced at all.
It immediately starts you out against level 18 enemies as basic encounters (in Chapter III) yet, bizarrely, also starts out with level 5 floor bosses. Over the course of all three quests, things never really level out with the difficulty continuously jumping around all over the place. Sometimes a boss will be a one-round joke, other times it’ll inexplicably be able to cast spells with multiple metamagic effects beyond its level or have 70+ AC or 30+ Saves. It’s just a massive slog in general and doesn’t really offer any rewards worth the effort besides a boatload of (effectively useless) gold and enough XP to get you to level 20 shortly after arriving in Chapter V.
Can’t speak for the stand-alone version yet, but if it’s anything like Kingmaker‘s Beneath the Stolen Lands DLC then it ~may~ be worth picking up if you enjoy playing around with different party compositions.
As an addendum, I also just ran through the content added by the free Love Beyond Death DLC. It’s… okay? While there’s nothing annoying about it, there doesn’t seem to be much point in actually wandering down there unless you happen to have a character specialized in Earth Breakers (since it includes the only +5 unique one).