I am very biased, but I've thought the Vikings have had a roster good enough to compete with GB the past few years and it just didn't come together. After Zimmer was gone it seemed more and more evident that he had lost the players. Not proclaiming the new coach a winner after 1 game but I wonder if just getting rid of Zimmer will give them a boost.
I lost all respect for Zimmer after he threw their kicker (Blair Walsh I think) under the bus when he missed a short FG that would have won a playoff game against Seattle. As I recall, they played the game in an outdoor college stadium because the Vikings were building a new stadium. The weather was below 0 that day and the field was frozen. Sure he probably should have made the kick, but it wasn't under ideal conditions. I don't think it won Zimmer much love among any of the players.
I also heard he and Cousins didn't have a good relationship. I've felt Minnesota was always better than what they were getting on the field and I think now that Zimmer is gone they may finally show it.