As patches go, the Enhanced Edition is about as good as it gets. Only once before have GameBanshee has seen a game get a major overhaul to its script and voice acting, and that game, Gorasul, desperately needed it (let's just say that it was poorly translated). The Witcher didn't really need to improve its script, but CD Projekt Red spruced it up anyway, and they made a lot of other nice changes as well, making the game even better than it was before.
Just be warned, though, that if you're downloading the Enhanced Edition as a patch, it's 1.5 GB in size, and since it touches so many files, it takes upwards of 2 hours to update your game. But that's a small enough downside given all of the improvements that you're getting for free.