As with all celebrity autobiographies, if you're a fan of the celebrity, there's a high probability that you'll enjoy the book. If not, you're unlikely to read it anyway. That's a point that's made often, but that probably bears repeating.
The structure of this book is slightly novel, in that it follows Mitchell on a walk around London, with reminisces and comic riffs inspired by things he sees along the way. I think it's fair to say that little of the content is deeply insightful: it's mildly embarrassing to buy underwear; membership of Footlights provides a firm footing for launching one's career in comedy; and most ideas pitched to television companies don't get commissioned.
That said, I like David Mitchell, so I enjoyed the book. The content isn't groundbreaking, but it is at least communicated with warmth and a degree of endearing self-deprecation. And I found the last chapter, in which Mitchell discusses his relationship with Victoria Coren, genuinely heartwarming. Others have described it as overly syrupy, but I disagree - I thought it was lovely.
It's hard to know what else to say, really. Mitchell comes across as a thoroughly likeable guy, and this is a highly readable but equally forgettable walk through a life that has been lived without all that much trauma, distress or heartache. It's a light read that, as a fan of Mitchell, I find it hard not to recommend. But it's hardly life-changing stuff.