I read the uncut, i hadn't read the original beforehand so i don't know if the added content is essential or not. King does mention in the introduction why this cut exists and i think most of it is just small character moments that he wanted to include.
I thought it was a good read but not great, like with most of King's books its the characters that kept me turning the page instead of the circumstances, however having read quite a few King's books now you do find that he endears most of his characters with the same traits and boy, does he love a good retard.
I enjoyed the epilogue to this one concerning Flagg.