Octavian is a remarkable man, one of the most capable statesmen in the history of mankind it would seem. However he was not flawless. There are two points which are very disappointing to me in his administration of the empire. Everything else he seemed to deal with perfectly well.

First was his military exploits. He cleaned up much, but the loss of a few legions in Germany somehow lost all his steam. Losses like these are bound to happen, but it was a weak reason not to continue the consolidation of Europe. Rome's military might was in one of its greatest phases, the barbarians still vastly behind. And he had the resources of the prosperity he created. Why not build a few less structures and finish off Germany and the northeast up to a suitable river, maybe to the Elbe? After this accomplishment later emperors could have pushed it to the Ukraine. In doing so you eliminate an enemy which festered over the centuries to become the conqueror. Additionally the border would have been simplified, after generations of subjugation of course. (I have nothing against Germans and Slavs...in fact I am one myself!) Of course I probably simplify the matter...perhaps it could not have been done, but if it could it should have been.

Also, succession. This could have been just as difficult/impossible to set up, but the Chinese seem to have had a pretty decent and reliable system themselves. Of course they had the benefit of cultural homogeny where Rome was an empire of many faces indeed. What could have been done to make succession certain? Could any system have been devised to avoid the woeful waste of emperors like Caligula or incessant civil wars? Come to think of it, I don't think mankind has ever come up with an answer for this one.