Actually, I think The Witcher is by far the best single character RPG I've ever played. I really don't know where you get the idea the system is designed for more than a single character, though. It's clearly not. Given the way combat is set to timed moves, you'd have real trouble with more than one character, don't you think? It had its problems, yes, but nowhere near the level of bugs that NWN had. The main problem with Witcher was horrendous load times, which were annoying but far from game breaking.
As for being MORE valid, I take it you do know that D&D is a system designed for a MINIMUM of four characters and preferably five or six, right? The classes are all balanced the way they are for that reason.
