I haven't read this cover to cover. It's divided in to three sections, about the literary culture of the time, the dating and authorship of works attributed to Middleton by the editors and textual notes about e.g. text variants and other detailed editorial matters.
I bought the book because I found, reading the Collected Works this volume is companion to, that I could not dispense with discussion of authorship, especially in cases of collaboration. On that front I have no complaints. The textual notes are not of great interest to me but I have little choice but to accept the editorial decisions made, anyway.
The section on cultural aspects of writing and distributing works in the era was a severe disappointment. The essays are clearly best suited to academic journals and use Middleton and his work as examples simply to justify being placed in this volume. I skimmed or skipped most of these 330p of essays, which could have been interesting if written for a general audience in similar vein to the essays introducing the actual Collected Works itself. I'm still using the book along side the Collected Works regarding authorship and general editorial aspects but I'm done with section I.