I'm sorry people don't like Julia McKenzie in the role. To be honest I was surprised when she was cast, because she's someone I didn't think old enough, though she probably is. This is an incredibly talented actress, who not only acts, she dances, sings, directs, produces all sorts of projects and is a general all-rounder.
I don't think there'll ever be a Miss Marple that fits in with anyone's idea from the books. Much like Poirot, who David Suchet took to his own, but Albert Finney probably inhabited better (though he was annoying). So whether you go for Margaret Rutherford's jowels, Joan Hickson's old 'bird' impression, Angela Lansbury's trying to get past some risible writing in the film, Geraldine McEwan's odd casting and the liberties they took with some of the plots, or Julia McKenzie's interpretation with some more liberties, it doesn't matter. The overall strength of Christie's writing, even when it's been through some very modern interpretations, still works. She never considered herself a very good writer, and there are some very odd moment in some of her books that wouldn't get past the PC brigade these days, but they last. And they'll probably still be remaking them with Amy Winehouse as Miss Marple in decades to come and Matt Lucas playing Poirot.
But I'm glad they're still making the series. Yes, they're not deep and meaningful, but they do provide a welcome break from reality TV. Go for it, I say. Unless they cast Katie Price in the roll, I'll still keep watching. And it's good to find a role that needs to be played by an older actress, who isn't still trying to kid the world they're still in their forties when they look like a trampoline under so much pressure one false move and their face could take out anyone in the vicinity.