I came here looking for a comment on isolationist policies (a wall around Britain - Brexit, anyone?), the effects of climate change and maybe also a philosophical view on otherhood. I can't say I didn't get what I was looking for, but it turned out to be a bit more shallow and pretentious than I expected.
Lanchester begins to describe a post-Change Britain, but he never finishes this job. There are one or two leads, but never enough to paint a full picture. The same applies to the world outside the wall - there are hints, but no real concrete descriptions of what the world looks like at all.
This can be a good thing - to let the reader imagine these things for him-/herself - but to be able to do that, we need at least some hints as to what this world has become. But all we get is a walled-in Britain, an ocean, a rocky island, a pirate ship and an oil rig.
If I wanted to be nice, i'd say it's like a combination of "The Road" and "Waterworld" outside the wall and some sort of artificial, unsettling version of a rural England on the inside. But that wouldn't be entirely honest. The truth is, it's none of the above. And unfortunately, there's nothing to replace that description with.
Reading this leaves me wanting more, but not in a good way. Hell, the book doesn't even have a proper ending!

But all in all, it's still ok. There's still a wall that's being patrolled. There are still Defenders guarding Britain against the Others. There's still treachery, catastrophe, pirates and post-apocalyptic settings to compensate the lack of depth. Lanchester does a fair job of following whatever writer's manual he has in his back pocket. But that's all there is. And I expected more than that.