The assault on Meereen as I remember it in the book wasn't that interesting... in fact I think that it was described by Daenerys only after it happened. But on the show, it was absolutely epic! I re-watched that single scene about five times.
OTOH, some great things about the book could never be replicated in the show. For example, you could never describe Tyrion's feelings about Tysha in the show, because it all happens in his head. I think that's why they converted Shae into a real character to replace Tysha, rather than her being just a whore