Now that Procopius has made his appearance, we can talk about him a bit more. While not the only person of the time who called out Theodora and Justinian, his Secret History is definitely the main work in the tradition. Procopius was secretary to Belisarius for a while, and then on his return to the capital was given various honors by the Emperor in recognition of all the wonderful toadying he did in his work on Justinian's public building projects. So, he knew the people he was writing about.
This explains a bit because Procopius, being close to Belisarius, would have a natural store of venom for the people who dicked him over, repeatedly - namely Theodora, Justinian, and Belisarius's wife Antonina. But he sees that Belisarius himself was responsible for opening himself up to much of the dicking, so that doesn't explain the full extent of Procopius's 190 pages of "These are the worst rulers ever ever ever."
Partly, it's that he was a conservative during a time when things were changing a lot. Justinian was combing over the laws to erect his massive code, and to Procopius, at his old-man-shaking-fist-at-horseless-carriage best, any deviation from the way things have always been is irresponsible meddling:
"When Justinian ascended the throne it took him a very little while to bring everything into confusion. Things hitherto forbidden by law were one by one brought into public life, while established customs were swept away wholesale, as if he had been invested with the forms of majesty on condition that he would change all things to new forms.... not because justice required it or the general interest urged him to it, but merely that everything might have a new look."
There is a whole paragraph on How The Kids Cut Their Hair These Days And Why It's Wrong.
So, there's a good deal of Old Coot Overstatement going on here, but that's not to say the analysis is totally off. Justinian's buying off neighboring tribes to, please, not attack us just now, was in retrospect a bad idea. Expanding the Empire back to a semblance of its glory day borders and then not paying the troops who did it - also not emperorship at its best. Only giving cities over-run by the very tribes he was buying off a year to recover before receiving the brunt of full taxation again (most of which was then going to be given to - yes - the tribes that had burned them to the ground -so that they wouldn't do it again?), didn't earn the affection of the people as much as he perhaps thought it might.
- Count Dolby von Luckner