Putting aside his clown show, Rex runs a complex scheme and, for everyone screaming about Barry's inability to adapt, Rex expects players to play his way. There was a mini-rebellion in Buffalo b/c they had a solid D under Jim Schwartz; Rex came in and changed the scheme entirely. After two years, the Buffalo D still needed time to adapt to the schemes that the Ryans run.
http://www.buffalorumblings.com/buff...-bills-players
Marcell Dareus: Rex Ryan defense was too complex for some players | Larry Brown Sports
In the two years prior to Rex, Mario Williams had 13 & 14.5 sacks; first year under Rex - 5.0; Maybe he dropped off b/c of age, but, the drop off was consistent with the entire D's performance under Ryan. After being 4th in both pts. allowed and yards allowed, in the first year under Rex, Buffalo's defense dropped to 15th and 19th respectively.
Rex ran a great D when he had HOF players. Since then, pfffft. He's all ego and clown show.
EDIT: More from last year -
Five problems Buffalo Bills players have with Rex Ryan's defense - Buffalo Bills Blog- ESPN