To evaluate something is to measure its worth. It demands considered judgement and analysis. To evaluate drama and theatre you must be able to recognise what was and wasn’t successful onstage and recognise all the elements that contribute to the impact of a production. If you’re writing about theatre it may be to evaluate your own work or that of others in a production you’ve seen. A written account of the strengths and weaknesses of a show is called a review.
If you’re writing about a live theatre production or submitting a review, you need to understand what this means. It’s an opinion and its job is to advise others about how good (or bad) something is.
People all have different tastes so opinions must always be justified. This means backed up with a clear example to support every argument. You must say why you did or didn’t like a particular aspect of the work. If you just give your opinion without a good reason others might not trust it. You would also need a thorough knowledge of drama elements, the drama medium and explorative strategies so you can note how they’re used in the work you’re writing about.
A critic is a man who knows the way but can't drive the car.Kenneth Tynan
Even professional reviewers of theatre (called theatre critics) rarely write wholly negative reviews. If they slated a production, (called a ‘hatchet job’), without evidence that they’ve searched for some positives, the reader might feel less inclined to believe them. Their review would then lack authority.
Steer clear of phrases like ‘I thought it was terrible’ or ‘I found it boring’. Not only will you sound unintelligent but arrogant too. Remember that you’re writing about the work of professionals who may have much more experience and understanding of theatre than you do.