All three of the large DLC released for the game are roughly the same size (more or less equivalent to the full scope of one of Neketaka’s districts) and geared toward an endgame party. Which is a bit of a problem since the level cap has not been increased… meaning you’ll spend even more time than before gaining tons of wasted experience.
The Beast of Winter is the first of them and is best tackled with a level 15-16 party, depending on difficulty (though if you want to face either of the two endbosses in combat you’ll probably want to be 17+). And make sure to pack weapons/spells that can do fire and/or crushing damage to have a slightly easier time clearing the opposition. Combat aside it’s notable mainly for adding an additional henchmen option and giving a number of interactions to Ydwin, raising her up to the status of companion during your time spent in the related areas.
Seeker, Slayer, Survivor is a very different sort of DLC and cannot be accessed until after completing the game’s main He Waits in Fire quest. So while the ‘recommended’ level is 16 you’ll almost certainly be closer to 20 unless you’re doing a low-level challenge of some sort. That’s a good thing though since the difficulty level varies wildly between fights, which can fortunately be triggered as many times as desired (a feature extremely useful for leveling the clutch of new DLC-added soulbound items), and you’ll definitely want the breathing room granted by the extra levels. SSS also enhances a particular henchman for the duration, but otherwise the only other notable feature is that the arena feels kind of empty and unfinished. The merchants in particular stand out with their low-level/generic equipment and the ‘guiding spirit’ is pretty annoying.
Depending on your choices in the prequel, the Forgotten Sanctum can be a bit tricky to start. Like SSS it requires He Waits in Fire be completed, but the Giant Wave event that triggers it doesn’t give you any information beyond ‘somewhere in the south’ and no quest gets added to your journal. A second event involving Llengrath is what points directly to the DLC content, but if you didn’t meet her in PoE 1 that event won’t trigger (having killed her dragons may also cause it to not trigger) and you’ll have to find the location yourself. Which, admittedly, isn’t very hard considering a large number of unexplored points of interest will have appeared on the relevant island.
Triggering it aside, you’ll absolutely want to be level 20 before exploring the new content considering the difficulty of the encounters inside and gimmicky bosses you’ll be forced to face. And as with the previous DLC, one of the available henchmen gets some expanded focus. Unlike those however this adventure is more… wordy I guess you could say. Atmospheric as well. It very much gives the impression of being a throwback to Baldur’s Gate II actually and fits in seamlessly with the default game.