If you've read one zombie apocalypse book, I've always said, you've read them all. I didn't know when I picked up Lifehack that it was going to be about zombies; had I known it, I wouldn't have started reading the book. And I would have missed out, badly.
The thing that makes these books special is the characters. They are, all three of them, real novels, teeming with the pain of the human condition, and yet always lightened by the author's wicked humour. You'll laugh, you'll cry, and you'll be occasionally grossed out - but gruesomeness is never slathered in merely for its own sake; there is an essential good taste to the writing of these books that makes them worthy to be considered independently of their genre.
Although my personal favourite is Watching Yute, I can recommend all three without reserve. They are all properly standalone, as a novel ought always to be; Picard is no amateur. Nevertheless, I read them in order, and as with any series, even the long series of the Waverley novels, I do think this is the best way to maximise one's enjoyment.
Find them, and Picard's other work, at AMAZON.