It was based on the Neverwinter Nights 2 engine, so the similarities to NWN are expected. Actually, from my perspective, combat in W1 was a big improvement over the turn based click and pray combat of NWN.
I liked Neverwinter Nights 2 -- so no wonder I liked playing The Witcher 1. I think I played on a very underpowered laptop back then (as a college student), so if the engine was sluggish I probably attributed that to gaming on a laptop :D