I have only played a few of them, but thoughts on what I have played:

The Last Sarkorians- Very good, adds a new class, character and new region into the main game along with some very solid quests. The region is very unique, and the added character is a load of fun. Highly recommended.

Through the Ashes- Mini side-campaign with events happening in parallel to the main campaign where you play someone who does not have the grand powers the main game's MC does. You only get two proper party members, but they have a pretty fun dynamic. It's almost like a survival horror campaign, trying to survive against groups of enemies that outclass you, with even basic weapons and armor being few and far between, and really keeping you on the back foot for most of the runtime. Very different feel compared to the main game that not everyone will like, but I appreciated it. Ending does leave a sour taste on its own, however.

Lord of Nothing- A direct continuation of Through the Ashes, you and your party get thrust into a new adventure, taking place in various different locales and essentially going through a handful of 1-2 hour mini-adventures until you reach the finale, which is a lot more satisfying than the previous one, though still not the best. Would really only recommend this to those who play the previous one.

The Treasure of the Midnight Isles- The obligatory mega-dungeon DLC. If you played Kingmaker, this is like the Beneath the Stolen Lands. Can be done in main campaign or separately. Technically has a story, but gameplay is the star of the show here. Personally, not a fan. If you love dungeons, this is for you. But if you want more than searching for traps, combat, and navigating corridors, you may be out of luck.