I replayed a bit of Kingmaker after WotR, and the writing has improved, IMO. In Kingmaker, it was sometimes just so horrid...
The background plot I felt was better in Kingmaker, WotR is pretty standard D&D fare, with demons and all that.
I'd still claim that WotR is one of the best D&D games, not because of the writing, but because of choices it starts giving you and how they're realized in the game. Spoilery stuff, so won't go into it too deeply.