Shirley MacLaine plays Endora, or rather plays the actress who is playing Endora. The film wasn't quite as bad as I'd feared, but it does misfire quite a lot of the time. The whole concept - "a movie about actors re-making a classic TV show" is rather flawed to start with. Nicole Kidman (as Isobel, who gets the part of Samantha) gives it a good shot considering the material (although her somewhat air-headed character is no match for the strength of Samantha). Will Ferrell is not the ideal choice for a Darrin (although if you are a particular fan of Ferrall you may get more out of the movie than most). Certain plot lines are not sewn up (is the actress playing Endora really a witch too? Does she have a fling with Isobel's dad?) And, also inexplicably, they mix up what is supposed to be "reality" and fiction, by giving Isobel an aunt who is identical to Aunt Clara in the series - and is even called Aunt Clara - it just makes a nonsense of the middle section of the film.
I went to see it in the cinema - enjoyed it slightly more than expected, but also saw many flaws - the music is good though!. Ultimately it has made me enjoy the original even more. Buy the Season One DVD boxed set - it's fab!