I normally wait for confirmation that a show's not returning before I post my review here, but with "Carpool Karaoke" now a year without new episodes and no word that any are coming I'm going to assume that Apple has had enough. Even if they do come back, the format is likely to be the same so I'd imagine my review will still be valid.
A pair, or more, of celebrities, actors or singers team up for a drive around a city and a sing along to popular tunes played over the cars sound system. Throughout the short journey the passengers gently interview each other, occasionally pushed along by a game or activity organised by the producers.
I should say, I've never seen the Late show version of Carpool Karaoke, though I was vaguely aware of it. It's only due to my efforts to try and see everything on Apple TV that I decided to give this a try. Whilst I'm not one of those people generally angry about the very existence of James Corden, I don't like him in the role here and am glad that he's only sporadically on screen.
It's the sort of show that, for me, either works or doesn't based entirely on who the guests are and whether they are left to their own devices or not. I'd say that almost every scene of a game played in the car, or sketch performed outside, is bad. Mostly, this is because they drag the spontaneity out of the show and then force an actor to try and perform without giving them chance to prepare properly. The best episodes, roughly speaking, are the ones with the musical kids, Lea Michele, Darren Criss, the Stranger Things cast, Ben Platt and Sara Barellies, as they're often the most natural performers. There are some funs ones with Bands mixed with a celebrity fans, such as Billy Eichner and Metallica, Fred Armisen and Weezer or Maya Rudolph and HAIM.
My advice is, don't do what I did and sit down and watch them all, but look at who the guests are and if you like them, watch it, otherwise skip the episode, and keep looking.