The expansion costs nearly as much as both Witcher 3 expansions, and CD Projekt Red explains why
Tl;dr; expansion pretty much change whole game, reworks core game mechanics and adds whole new district. Plus Idris Elba and more of Keanu with expansion having almost as much lines as core game.
I can see why people would be at least skeptical given the way the game released. And while they keep reworking the game mechanics the core game story and vibe is pretty disappointing.