How good is LSU's defense, really?

I will admit that I haven't watched as much of LSU as I have wanted to. I saw them play the entire game against North Carolina, a half of the West Virginia game, a half of the Tennessee game and a half of the Florida game. However, I have not really been that impressed by their defense.

Sure, they do rank 3rd in the country in total defense, but they also haven't really played many teams with an offense. Their schedule thus far, with total offense rank in parentheses:

North Carolina (63)
Vanderbilt (102)
Mississippi State (55)
West Virginia (64)
Tennessee (97)
Florida (91)
McNeese State (78 in FCS)

The best offense they have played thus far is a mediocre Mississippi State one.

We all know that Auburn's offense is one of the best in the country, and LSU will be the best defense they have played, without a doubt, but how good is LSU's defense, really? Someone who has seen them play more please inform me.