Margot Heinemann wrote Puritanism and Theatre: Thomas Middleton and Opposition Drama Under the Early Stuarts, a book which largely seeks to align Middleton with what she terms "Puritan Parliamentarianism." She argues that Middleton's plays are part of "opposition drama," a movement in later Jacobean theatre that was anti-establishment, anti-Laudian, anti-aristocratic. She attempts to reconcile the plays of his early career (satirical comedy) to those of his mid- and late career (tragi-comedy and tragedy, respectively) by seeking out a through-line motivated by religion and politics. She also asks how A Game at Chess could have possibly been approved by the censor and produced on stage when it was so obviously a satire on contemporary royal policy.
Her first chapter, "Time and Place," is great; a short and pithy introduction to the economic and political situations of the day and drama's place within them. Her second chapter covers, and dismantles, the traditional assumption that all Puritans were militant anti-theatricalists. The remaining chapters on Middleton discuss his plays, grouping them chronologically and connecting them to major themes and issues taken up by opposition drama, such as Popery, the hopeless state of the poor, the excess of the rich. Hengist, King of Kent seems to show, through the lens of a long-ago British history, the dangers of King James' dalliance with the Spanish, as well as the current wool over-production and how this affects the farmers and peasants.
I was not very convinced, though, by a chapter entitled "How Anti-Puritan are Middleton's City Comedies?" in which her major argument seems to be, When Middleton is making fun of Puritans, he is actually just making fun of all hypocrites, not Puritans especially. One of the reviews I read took her to task for that as well. Her book is also working on the assumption that Middleton is definitely Puritan, a view which Heller disagrees with. Finally, she disputes the authorship of The Revenger's Tragedy.