I'm a fan of John Mulaney. I'm a fan of (some) late night comedy shows. This was definitely a different format than anything I've ever seen on any late night show - but it worked. The pace is just right: switching contexts every 5-10 minutes between John Mulaney monologue, guest banter, correspondent bits, and calls from guests with funny stories.
I'm honestly shocked the ratings aren't a lot higher. I usually have a much higher bar for comedy shows than others and this was entertaining start to finish IMO. If you're expecting a more politically charged show like John Oliver's Last Week Tonight, then this show won't be for you. If you're expecting an intellectual discussion, this show isn't for you. If you want to be entertained and you like John Mulaney's humor, this show's for you.