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.
So did you ask how the empire managed to survive as long as it did. I've come to the conclusion that it was so partly out of a power vacuum elsewhere and that when things got real bad, they would luck out and find an emperor who wasn't so bad, long enough to patch up the old rusty bucket. Of course they'd kill him and the cycle would start over again.
I'm still amazed it lasted as long as it did.