There is no question that Kubiak is a very good offensive coach. While in his first go-around in Denver he largely did not call the plays (that would have been head coach Mike Shanahan), he played a key role in helping to build some explosive offenses, particularly those that helped the Broncos to back-to-back Super Bowl championships. He also excelled as a playcaller during his tenure in Houston, made Matt Schaub look pretty good for a few years, helped Arian Foster develop into one of the elite running backs in the league and brought out the best in Andre Johnson. He also uncorked the best offense statistically in Ravens history this year as they finished 12th in the league in yards and eighth in points.
And Kubiak's prior head coaching experience was not unsuccessful (forgive the double negative). While the Texans were slow to develop, he did lead the Texans to their first playoff appearances and their first playoff victories and that does count for something.
But Kubiak's teams also had reputations of not meeting expectations, even in the years when they did make the playoffs because they were considered to be potential Super Bowl contenders. Considering that Fox was essentially fired for not meeting expectations, namely not winning a Super Bowl, bringing in a coach whose teams did not perform to their potential may not be the best of ideas, even with Kubiak's extensive ties to the team.
Also, can Kubiak make this team better? Peyton Manning's decline late in the season really seemed to sap some explosiveness in the Denver offense, even as C.J. Anderson broke out as a playmaker in the running game. Kubiak is a very good playcaller as already noted but can that mask further decline from Manning, who may not even be a sure bet to return next season.
To be honest, I really do not love this hire. Sure his past coaching experience had some success but it seemed like what really brought him back to Denver was his prior connections to the franchise and specifically to Elway. And is Kubiak really a better head coach than Fox was? I don't think so and I think this hiring will eventually make Bronco fans yearn for Fox.