Yes, Rome was a great civilization.
You may doubt that decadence and corruption brought about the fall of the Imperium Romanum, but just look at what happened.
After the death of Commodus (180-192 BC), there were four emperors the following year: Pertinax, Didius Iulianus, Niger and Septimius Severus (the latter two proclaimed emperor at the same time). Septimius Severus defeatet Niger, and later, a further rival, Clodius Albinus. He reigned until 211, when his sons Geta and Caracalla succeeded him. Geta was murdered, and the cruel Caracalla reigned until his murder in 217. He was succeeded by Macrinus, Elagabalus, Severius Alexander, and Maximinus. Now we are in the midst of a period between 235 and 284 in which there were several dozens of self-proclaimed emperors struggling against each other. During the same time, foreign aggressions -Goths, Persians, Allamans and Francs to name some- weakened the Roman border because Rome was too much concentrated with itself. During this time, there have been some strong emperors who could have resurrected roman power -Claudius II, Aurelianus- but their lives ended too soon. And when Diocletian finally became emperor in 284, Rome was already so weak that all efforts to resurrect it failed. Diocletians plan failed with Constantine. Constantines empire died with Constantinus (361). It all adds up to each other and all the time, Germanic tribes were gnawing on Rome's border. Rome just didn't counter with strong leaders, and if, they were still unable to prevent the eventual disaster: the coming of the Huns in 375 and the great migrations into the Roman empire. Negotiations failed either because Rome was too stubborn or the emperors were no good diplomats. Diseases, yes, they spread, and they might have added to this as well. But we cannot deny the obvious. Rome fell because it was unable to govern itself in the end. It was too large, perhaps not so in area, but it was too complex! A widespread disease like the black death in the middle ages might even have saved Rome from its fall, because in the end, there were too many people in the empire, too many different people, Rome was a chaos. The efforts of certain emperors to resurrect Rome even hastened the fall because their models left ruins others did not dare to remove or build over, so they built new buildings (in it's own sense) that weren't finished either.
In the end, the fall of Rome was inevitable.