I've read Gibbon and it took a long time, but it's not hard to see why it was controversial at the time. His description of the early church was quite objective and therefore rather uncomplimentary.
BTW, it's still very much worth reading. It's full of facts, so probably not for some of the crowd.
I own it (of course) in three volumes, but I've only read portions of it. The first volume is the best, in my always humble opinion. I agree with an earlier poster that the tag-end of the empire is pretty dreary reading, although it's an amazing catalog of horrible government. He's not very complimentary about the role of Christianity. Will Durant (yeah, I've got that whole set) is probably even more harsh in his opinions.
I don't care what you say. I didn't descend from a Gibbon.