They are excellent fast food burgers. But they're still fast food burgers, so go with those culinary expectations in mind.
Good value, too. And I like the simplicity of the menu -- kind of a nostalgia thing. And some of their locations have extraordinarily conscientious staff for a fast food restaurant.
I wouldn't pass up a gourmet meal for In-N-Out, but if I'm eating "on the run" in SoCal (they even have some stores in AZ), I'll look for an In-N-Out over the competition.