[Update #2]: Pathfinder: Wrath of the Righteous' The Lord of Nothing DLC has added 15 new archetypes and a lengthy side-story to explore.
[Update]: Pathfinder: Wrath of the Righteous' Enhanced Edition has landed with new quests and improvements.
Unlike the last two DLCs that mostly focused on telling new stories, the freshly released The Treasure of the Midnight Isles expansion is all about the gameplay. The star attraction is the brand new and challenging roguelike mode you can dive into as a standalone adventure or as a part of the main campaign.
As befitting its roguelike moniker, The Treasure of the Midnight Isles will allow you to explore a vast array of builds and party compositions as you venture across the foreboding archipelago, plunder all sorts of magical items and consumables to help you along, as well as fight against scores of old and new enemies. Most importantly, with each run you will slowly uncover the secrets of the Abyss, and with it the truth about the magnificent treasure that awaits you at the very end!
What all of this looks like in actual gameplay, that you can get a pretty good idea of through the freshly posted launch trailer. Have a gander:
As a final note, I feel it's important to once again reiterate that The Treasure of the Midnight Isles is a mostly combat focused DLC. While it does have a storyline and a mystery for you to solve, the actual focus is on giving you a playground in which to explore a variety of different and potentially spicy builds. So if you're planning to dive into The Treasure of the Midnight Isles, make sure you're doing so because you're itching to see just how far you can get with limited resources and a seemingly never-ending stream of foes.
To learn more about The Treasure of the Midnight Isles, as well as to check out some of the player reviews, you should hop on over to Steam. Enjoy!