WWE needs to be very careful in how they book Reigns. Frankly, they need to give him the Cena SmackDown build: a slow, steady build where he flirts with main event status constantly, but is positioned as the leader of the mid-card. John Cena was insanely over from what I recall (then again, I was just an ignorant teenager at the time) throughout his Smackdown run because WWE didn't give him too much, too soon. It wasn't until they moved him to Raw, started cutting back his character, and put him in matches against respected veterans that the audience really turned on him.
Reigns has potential to be a major star if WWE is just as careful in how they build him up.