Their run defense is very bad... but they've improved dramatically since their bye week in almost all other categories. It's been well documented that their defense is young and inexperienced (most of their starters are in their first or second year in the NFL) but despite struggling early on, they've been performing well --- winning seven of their last games incl. the postseason, and holding their opponent below 22 points in six of those wins.
I wouldn't say these are elite numbers, but it's a solid defense that complements the kind of football Atlanta is playing -- a defense that can protect large leads, generate turnovers, and get after the quarterback.