I came here (fully sober) mid day on a Friday. The place wasn't overly packed but still a good amount of people were there. I've never had a Fatburger mostly because all of the ones I know of in the Midwest closed.
We split a L burger and fat fries. The fat fries are what most places call "steak fries" they were really good and freshly made. We ordered the burger the way they normally make it and add cheese. The burger was decent but nothing life changing. It was heavy on the mustard also.
It took 20 minutes to get our food, which was longer than I expected but it wasn't that big of a deal.
I've heard this place is great when you're drunk so maybe I came at the wrong time