>Whats christians opinion on the fall/rise of roman empire with its connection to Christianity?
I think a lot of people try to correlate Christianity with the fall of Rome, which from a historical perspective is not correct. The fall of the Western Roman Empire would still come, even if they had converted to the most violent Pagan religion or Hinduism. This was ultimately dependent on their geographical positioning and the social/economic situation. The same case is for the Eastern Roman Empire or the Byzantines.
>Do you think Christianity was good or bad for rome?
It is a good thing! We (of course) believe Christianity to be the truth, but the Western Romans adopting Christianity made the transition from the empire into smaller kingdoms a lot easier. The Church here in Europe has always been the center of learning and knowledge, they basically have kept this continent running since the beginning. The same applies to the Eastern Roman Empire.
Looking at Europe after the fall of Rome, we can see the common factor which actually kept the continent going and repelled invasion after invasion (from Muslims) was the Church. A lot of secularists will try to ignore this today, but the reason Europe has come out on top today in terms of science and prosperity is because of the constant pushes it got from the Church over the centuries.