Anyway, the germanics raiding and entering the empire in large number wasn't the only problem, but it was the problem that made all the others problems worse. It wasn't the only factor that led to the fall of the Empire and to the avent of the dark ages though. I agree with that. Christianism played its part, plagues, economical recession and civil wars too. But all of those may not have lead to such a radical change in the roman way of life and to the social organisation if the germans didn't became the new masters.
Not to say the germans are bad... There are no real good and bad guys in this story. Germans may even have been the good guys on some occasions. What matter is the result.