It's a hard tone to maintain. Gretchen and Jimmy are complete assholes who really don't deserve any sympathy, but the show actually makes me feel for them. It's as if their issues are really the cause of their behavior.It looks like a louder, more obnoxious version of You're The Worst.
I just started watching this for the first time this season, and I'm loving it. It's nice how they actually deal with the characters having serious issues, and manage to find humor in their situations, but aren't necessarily making fun of people with psychological problems.
Except for Lindsey, Lindsey is an awful human being. She's actually the worst.