Celtic society became Romanised. The glimpses of an independant Celtic nation show that they adhered to Roman institutions and modes of government.
The tenure of their Emperors was just as unstable as that of the Roman Emperors themselves. the two parallel systems were so similar that it becomes difficult to distinguish between them. It is possible that some Roman Emperors saw themselves as Celtic first and Roman second.
Then again, their were differences imposed by the emergence of Christianity. in general the Celts adhered to worship of traditional gods and their version of christianity was substatially different to that promoted by the Church of Rome