Critics and theatre directors alike have argued that the inclusion of the slides was and would have been unnecessary for the action of the play can and should be able to speak for itself. The strength of the dialogue and the characterization alone tells the story. As they can be a distraction from what the characters are doing on the stage, I can easily see how they would be a distraction, particularly for an audience that was not accustomed to that sort of convention. However, on the other hand, as Tom was a writer and this is Tom;s story, I think you could also argue that the slides might be representative of the story that is playing out inside of Tom's head in his memory. They are very cinematic, and with Tom;s connections to the movies and his love of escaping from the apartment that serves as his prison there is an element of dramatic narrative that could be played our on these slides. They can create an almost split focal perspective - which can be either a good or bad thing depending on how they are implemented.
Some theatres have integrated the use of slides effectively. Kansas City rep, for instance, updated William's original concept through projected cinematic imagery and integrated it into the action of the play to give the play a "new" interpretation that stayed faithful to Williams' original concept (see review). The Broadway revival, on the other hand, has been criticized for integrating the device as a full curtain which served to conceal so much of the action that it ended up being a distraction, (see review).
As a director, I have directed the piece without the inclusion of the images, and I have worked on a production in which they were included. The biggest problem with them is that, although they can serve as a glimpse into Tom's writers' mind (as the play is autobiographical, this can be useful) they are often more distracting than driving. They tend to split the audience's focus, and that can be dangerous.