Don't read this all at once. You'll get indigestion. It's eighteen largely disconnected pieces, not a narrative. Cinema Purgatorio was actually a comics anthology series from Avatar Press. Moore and O'Neill did eight pages per issue, with other contributors including Garth Ennis, Kieron Gillen and Christos Gage.
What I have is merely a collection of the Moore/O'Neill episodes. They're ingenious and shocking, but often not even fiction. (Moore's done that kind of thing before, e.g. Brought to Light, with Bill Sienkiewicz.) Despite their imaginative presentation, they'll be telling stories that you might even already half-know. The Black Dahlia murder of Elizabeth Short in 1947. The blurred lines between Hollywood and the mob. The film stars who slept with extremely underage girls. The acquittals that were arranged for drunk drivers who'd killed. Issue 4 tells the appalling story of Willis O'Brien, narrated by his most famous creation, King Kong. (Had it been fictional, you might not have believed it, but it's all true.)
I learned amazing facts. Apparently, more people died in Eisenstein's recreation of the storming of the Winter Palace than in the original battle.
Sometimes, though, Moore lets his hair down. There's an episode about those black-and-white cliffhanger serials and their grossly cheating cliffhangers. I loved Moore's demolition of these. (I think for forty years I'd forgotten how much those bugged me. I'd accepted them anyway because they were old, I was young and they were on BBC2... but bloody hell.)
Moore also puts the boot into the UK's Children's Film Foundation. Personally, I'd never particularly rated those films, but I'd also never really thought about them since I hadn't been old enough to see them in cinemas. Moore and O'Neill speak from childhood experience, which doesn't appear to have been good. "The results were always so bland. Did anyone love them, do you think?"
This book is fascinating, but don't binge it. Dip in and out. Read the odd episode, then google "Cinema Purgatorio annotations" and look up all the footnotes, references and history. It'll be quite a time investment, but it'll be worth it. This is a rich read. Laugh at Moore's games with Ben Hur. Recoil from the biography of Jack Warner (the president of Warner Bros, not the British actor who played Dixon of Dock Green). Ditto with Old Mother Riley, aka. Arthur Lucan. (Note to self: one day, I must watch some of his movies. I also really wish he'd got to make Old Mother Riley's Trip to Mars...)