The possible lesson here, IMO (and also from Tyranny even though it isn't technically a sequel): Less grimness. Audiences have had enough of GRIM WORLDS WHERE YOU WILL MAKE GRIM CHOICES.
Big, bright, colorful worlds don't even need to tell you you'll get to make choices. They seem to inherently convey escapism, freedom and possibilities. The open-ended sea exploration aspect of PoE2 bodes well in that respect, but you'll have to emphasize it.
So, you're saying Obisidian needs a Colour revolution?
As for the D:OS2 success, I'm not surprised, Swen is an infectious character and his Kickstarter vids were on point and entertaining. Feargus needs to go to CEO school of Swen.
Infinishill clearly hasn't played the game. There's a quest line and entire level in Act II that is legitimately disturbing, more so than in any CRPG I've played.
And incidentally better than the entirety of POE.
Edit: it'll start being old when you shut the fuck up about Tyranny.