Fourteen years is a long time at any job, but especially as an NFL head coach. Mike Shanahan hadn't replicated the great success of his two Super Bowl wins of the late 90s, hadn't even come close in a long time. And just when he seemed a cinch to put the team in the playoffs for the first time in 3 years, he pulled a Norv Turner, his team crashing and burning in spectacular fashion on Sunday night.
Denver, like Washington, is a football town. I remember in 1989, the season after the Redskins beat Denver in the Super Bowl, a Redskins pre-season game won it's time slot in what the WaPo,'s TV critic dubbed, "The Redskins devour everything in their path." Denver's pretty much the same way. The town put up with B+ teams for a decade only because of those two Lombardi trophies.
Coaches with total control, who double as GMs rarely do well. It's almost impossible to be both good cop and bad cop at the same time to the same player. Instead of working with what they have, they have to divide their attention with getting more. They'll fall in love with personnel decisions that are a mistake. (Some of Joe Gibbs's biggest blunders came when he demanded particular players. Almost certainly his success the 2nd time around was limited by the lack of a strong GM like Charley Casserly or Bobby Beathard.)
Still, those two Super Bowl wins, numerous playoff appearances, they count for a lot. Towns with winning teams tend to forget how hard it is to get there, and how long it can be between successes. Shanahan's time was probably up. But we should appreciate what he did while he was here.