I enjoyed NWN 2 up until the castle. After that, things fell apart in my opinion.
I blame it mostly on what they did with Black Garius. Instead of getting the fulfillment of facing him in combat, the weird ritual changed him into something else. I felt like that was a huge mistake, denying the player closure with that villain.
Same with the ambassador Torio. Having her executed or taking her on as an advisor just wasn't as fulfilling as wanting to face her in combat at some point.