I'll play Devil's advocate. Under RR, WVU was 2-0 in BCS games beating both Georgia and Oklahoma (no, Oklahoma doesn't count for Stewart, it was RR's team). He won 4 Big East conference titles in 7 years at WVU. He posted a 3-0 record against the SEC, 1-0 against the Big XII, and an overall winning percentage of .66 against BCS teams with, for the most part, second tier talent (Rivals average of 2.54 stars from 2002 to 2007 inclusive, only 6 players drafted during his tenure - 1 player undrafted and playing in the NFL). He had exactly 1 5-star (per Rivals) recruit during his entire tenure at WVU, and that was Noel Devine. RR doesn't have the stellar record of a guy like Tressel or Carrol...or even Stoops...or Meyer...or Miles...or Richt...but his record isn't as bad as everyone would like to believe.
That being said, I think he may have issues with the transition. His system will eventually work, but it's going to be a culture shock. Michigan is the Republican Party of college football: they fear change and do everything the same way they did it in the 50's. He new-fangled-old-timey-modified Wing-T Triple-Option bastard child offense may raise too many eyebrows for his own good.