The first thing you must decide is whether you are looking for a play review or play criticism. A play review is written in reference to a particular production. The content is mostly concerned with introducing the plot and evaluating the quality of the actors, sets, costumes and direction of a specific performance.
Reviews tend to be very short, usually less than a page.
Criticism looks at the play in a larger context. Beyond a mere recounting of the play's plot, a critical article explores the subtext and deeper meaning of the play. It may discuss issues of symbolism, character analysis, linguistic styles, and placement within a particular genre. Criticism rarely analyzes a particular performance, but typically focuses on the printed text of the play. These articles usually run between 5-20 pages in length.