For me its quite clear what went wrong with PoE 2, it is direct sequel. Many people havent completed first part so starting direct sequel feel quite uncomfortable. Situation would totally different with another hero and story. Setting and lore is so great in PoE soni really hope they will make more PoE games. We just need a another hero.
Of course there were some quite derious flaws. Difficulty was balanced very poorly, games being much too easy. And on hardest difficulty levels game just start to feel like work, not challenging, just boring work. Another thing, when you playing cr