They made him the stereotypical "bad boy with a heart of gold." They took his edge from him and made him far less interesting. That is exactly what happened with Dean Ambrose.
That's not my only issue with Ambrose as I find most of his signature spots to be contrived and goofy, I think he hams it up a bit too much as well, but The Fonz vibe really kills him.
There is some good news though. It seems since he lost the title we've gotten a much better version of Dean Ambrose. He's got his edge back, and if he continues to do promo work like he did on Talking Smack, he is far more interesting.
My hope is that this new and improved Dean Ambrose continues. Only time will tell.