Bittersweet comedy helped immeasurably by the chemistry of the stars and the skill of their performances. Glenda is brash and delicate in equal measure, George bombastic but good natured. While it shows the pitfalls of infidelity it doesn't judge its characters for their choices and actually presents all the relationships, including Glenda's gay assistant's, evenhandedly rather surprising for the 70's. As far as her receiving an Oscar for this performance, she's sprightly and more relaxed than she usually was on screen but I doubt that even she expected to grab the prize for what is a customary solid job but hardly extraordinary.
Review of A Touch of Class
