Rob Ryan has been seen as a blowhard and a loudmouth by many football fans, but to be fair, there's no evidence saying he is a sociopath like Gregg Williams. Gregg got away with far too much during his time with the Saints and it cost everyone involved. Rob Ryan, or anyone for that matter, who intends to work for the Saints will have a very short leash in exchange for working opposite the NFL's premier offense.
That leads me to another angle on Ryan. We may look at his former teams and their statistics and feel quite underwhelmed but let's look at what types of offensive leadership his defenses had to make up for.
Oakland 2004-2008 QB's: Kerry Collins ('04-'05), Aaron Brooks ('06), and JaMarcus Russell ('07-'08) Head Coaches: Norv Turner, Art Shell, Lane Kiffin, and Tom Cable
Cleveland 2009-2010 QB's: Derek Anderson ('09), Jake Delhomme and Colt McCoy ('10) Head Coach: Eric Mangini
Dallas 2011-2012 QB: Tony Romo Head Coach: Jason Garrett
You could combine all of these quarterbacks into a Voltron-style mega QB and still they couldn't come within 100 yards of Drew Brees' talent, heart, and leadership. When Tony Romo is the absolute best quarterback you've ever had opposite your defense it's not saying a lot. So clearly Ryan hasn't had a lot of backup over the years and his defenses have had to do a serious amount of compensation and load carrying.
Rob Ryan paired opposite Sean Payton and Drew Brees on offense could potentially be an intimidating combination for the rest of the NFL to prepare for. Although Ryan is a long-time 3-4 disciple (which is ideal) the 4-3 is not foreign to him from his Raider days.