It's a pisstake of Kirkman's The Walking Dead, written by Kirkman himself based on one of his original pitches to Image Comics. His first proposal had been a straight zombie series (set in Romero's Dead universe), but Image ultimately rejected it as too "normal". Kirkman then resubmitted it as an alien invasion story, with the zombie plague being an alien bio-weapon. He assumed (correctly) that after getting greenlit, he could ignore all that and just write what he'd originally planned.
Here, though, is an Imaged-up version of the alien nonsense. It has silly superhero dialogue. Rick Grimes has a leotard costume and a lightsabre. It gives the Governor a cape and a robot pincer claw hand. Eugene becomes Dr Octopus. Characters get resurrected left, right and centre because comics do that all the time. Lump-in-the-throat emotional moments get bastardised into macho catchphrases.
It's horrendous. And it's brilliant. I laughed and laughed.
The best things about it (for me) are the bits that are unexpectedly faithful to the original. Martinez having mixed feelings about Rick killing him and pointing out that the bad thing he'd wanted to avert had ultimately happened anyway, so the murder achieved nothing. A character who died before meeting Negan says "what's a Negan?" The Whisperers. The cameos. Rick Grimes correctly becoming Mr Avuncular Big Beard. All that I loved. Without those, this book would have just been loud silliness that didn't really connect to anything.
Negan, on the other hand, felt slightly off to me. He's stuck in "manic super-swearing villain" mode, as per his earlier appearances. This is okay, I suppose, but I don't find him as funny or memorable as later Negan. Ah well.
But never mind. This book is ridiculous, surprising and funny. What more could I ask for?