To understand why 2012 boasted a weak field of presidential candidates you must understand the influence of money in politics. Romney had either lined up most of the big money, or neutralized it. The people who would have backed a Chris Christie were already backing Romney. The only real money threat came from Rick Perry. The threat was significant, but the candidate himself was not. Romney was challenged on ideology by Santorum and Gingrich. Gingrich had a real shot but lacks focus. He could have put together a winning campaign but over thought his campaign every step of the way. Santorum didn't have squat for cash, but focused on the basics and proved to be tough opponent.
I'm of the belief that the 2016 field is basically set. In my opinion it is the strongest field of candidates Republicans have had in a while, and I'd bet money of them will be elected president.