Yes, I absolutely expect to be entertained when I go to the theater, however, that is only one of many expectations that I have. I also want to be engaged.
There are many ways to engage a person and each person is going to find different things engaging. For myself, I want my brain to be engaged. If you can engage my emotions, that's a plus too. For me, a fine night at the theater is when I've found myself presented with ideas that I have to wrestle with or am given a new perspective on a familiar issue. I like plays that continue to unfold after I've left the theater, forcing me to continue to examine layer after layer. I'm especially fond of shows where there aren't clear-cut answers and I am left pondering and arguing more than one side of something.
Notice those past three paragraphs have a whole lot of the word "I" in there. It's intentional. Nothing in those paragraphs say "this is what makes good theater" or "this is what art is." Rather, they state what my personal preferences are. When I am in the role of critic, it is, quite frankly, irrelevant what I like or dislike or what my preferences are. Why should any of my readers care whether I like a show or not?
My Personal Opinion? Why would you care?
"Isn't that the point of a review? It's an opinion, isn't it?" you might ask. (Or maybe you wouldn't, but indulge me a moment, please).
I would argue no. I mean, yes, it's an opinion and an expression of subjective criteria. But whether I liked it is NOT the point of the review. The point of a review is whether you, the reader, would like it. Most likely, you and I have different tastes in at least some aspects of theater. My telling you I like or don't like a show gives you no information on whether or not you would like or dislike it.
While a review expresses opinion, that opinion should be supported by specific observations--observations that can help you to judge for yourself whether you liked or disliked a show. I may hate farces (I don't, but let's pretend for the sake of argument that I do) and you may love them. If I'm reviewing a farce, I shouldn't be complaining that the acting was over the top or the situations unrealistic. Rather, I should be critiquing whether the play lived up to the conventions of a farce or, if it broke those conventions, whether the choices were effective for the genre and for the purpose of the play. If I've written the review well, the reader really shouldn't know whether I liked the show or not.
I've found that I rarely give a direct answer to the question, "Did you like the show?" More often than not, I'll give some specific reply about what worked or didn't work in a show rather than express my personal pleasure or displeasure--that is, if I'm talking to someone in a professional context.
To be honest, it is the elements of a show that I find far more fascinating to talk about anyway. To say I "liked" or "disliked" it seems so final, so pat. It lumps everything I've just experienced into a single word. Most plays deserve far more than that. They deserve to be heard, to be listened to, to be discussed.