Just before Caesar came along and get into a fight with the Senate. Congress' approval ratings are so low it really wouldn't take much for a powerful populist movement to challenge the constitutional makeup.
...Although a part of me fantasizes about the freedom which existed in Dark Ages....
You might want to check folks approval ratings of their own congressperson. The overall rating is horrid, but the "mine" is generally quite good.
The eastern half thrived, and even reconquered Rome and Spain, under Justinian. This was a continuation of the exact same government, no fall from power, just a loss of some territory. They lost Rome back fairly quickly and were controlling various parts of the Eastern Mediterranean, Eastern Europe, the Middle East and North Africa on and off until they entered terminal decline after 12-1300 or so, and Constantinople finally fell to the Turks, with the last Emperor dying in the battle in 1452.
But they had a much harder time dealing with the huge influx of displaced Germanic tribes due to the (Mongols iirc?). The western half of the empire started down the road to things like castles and other behavior like large estates that directly fed into the middle ages. Diocletian and his division of things into dioceses also helped, but I think once they started down the path of dual Augustus/Caesar rule it was bound to fail due to the inevitable clashes of personality.
That said its a great story. A good overview of things is in the "History of Rome" podcast. http://thehistoryofrome.typepad.com/
Its long, but not as bad as The Decline and Fall of the Roman Empire. That book, the horrors.