The most regrettable decision was the long field goal in the first Minnesota game. It was not an easy call, but you hope your kicker can make a 54 yard FG in a dome. And, frankly, how do you know if you can trust your kicker if you don't put them in that situation? You wouldn't want to put the whole game on your kicker's shoulders either, so you test him like this when you have the lead. Unfortunately he missed (and got cut).
Even though we can wish Campbell went for it, the real scapegoat in this situation was the secondary who gave up 56 yards and a TD in two plays.
Anyway, Campbell deserves to be at the top of every coach of the year ballot, and if he coaches the Lions to a Super Bowl victory he will become a coaching legend. Sheila and Rod and Chris Spielman nailed it with him, despite all of the complaining that they should have hired a GM and let the GM hire his coach.