Maybe it's just my perspective since I exclusively play as a Tank, but RPB might just be my favorite Dungeon in this game.
The level design is awesome, the mechanics are amusing, and the bosses are actually fun? Even the side stuff like fighting the secret bosses and getting their rewards were a blast!
And none of the bosses had terrible mechanics. No "Insta-Kill if you don't do this" garbage, no serious DPS or Heal Checks. Just "pay attention and your life won't be frustrating." Hell, the first guy with the Goat magic actually had me and my group laughing!
It's such a departure from the frustrations of most other DLC Dungeons. The Dread Cellar and it's nightmare of micromanagement on the final boss being a good example.
And I understand that some people want a "real challenge" when it comes to this stuff. Something that makes them want to drive their fist through their monitors. I get it. But that's what each boss having a hard mode is for now! And if that's not enough, then I'm sorry, but wanting to have a difficult experience shouldn't make things miserable for the rest of us.
Tldr: Red Petal Bastion was incredible and I hope to see more content like it in the future.