I'm convinced that it isn't O'Reilly, but his format that is the winning formula.
People were so sick of these empty Crossfire/McLaughlin Group model one or two hosts/two to four soundbyte-barfing guest Chinese fire drills that reveal nothing that when O'Reilly's lively one on one format debuted in Prime Time, it was compelling.
Unfortunately, O'Reilly is morphing into Chris Matthews.
I always said perhaps the most spellbinding show would be Alan Keyes hosting an hour long "one on one" with Jesse Jackson/Kwese/ACLU/NOW/NARAL/GOPDEM/GayLesbo type guests/representatives. One hour with Alan. Watching him destruct the evil spawn would have been an epipheny. Instead, they threw him into the same "one righty/one lefty spewing talking points for 6 minutes" crap we see everywhere else. Now we watch him flounder in Illinois.