I think the book is bawdy and the score is tuneful and witty... I think many people didn't find them to be the perfect match. I think the show as a whole is wonderful. But I don't think Sondheim's score is very coarse at all, maybe to a fault. Though clearly not since it was met with a lot of success when they combined the book and score.
I don't know what people these days think, but I've always heard and agreed that the Forum book is one of the best musical books out there.
