So did I accidentally kill film club?
I rewatched The Stone Tape and it still holds up. Jane Asher flips between hysterical and coldly scientific and back again a bit quickly in the first act for me, but once everything is set in motion it all works.
Has the standard Kneale message of "leave well enough alone" but unlike a lot of his work, and almost all of the MR James stuff that inspired it, Brock is not just unlucky or innocently inquisitive. He's ruthless and cares only for himself, and all the misery caused can be placed squarely on him. His descent into madness is caused not be the supernatural, as in Jill's, but by his ambition and the hole he digs himself into with Ryan.
Jill herself isn't actually a particularly strong protagonist in my opinion. She's very reactive, dragged along by the others while doing little but beg them to stop. In that way she's very much the insert for the audience. Just like in "Baby" or "Quatermass and the Pit", the audience is screaming at the characters to stop what they're doing before something terrible happens, and Jane gives voice to that.
Actually, Baby highlights a few of the other nitpicks I have with The Stone Tape. In Baby there's plenty of talk of the supernatural and certainly some hints earlier in the short, but it never explicitly shows anything. In The Stone Tape the ghost walks right at the beginning, removing that ambiguity. It's understandable given that the story is not about whether something is happened, but how it is happening, but when it comes to raising tension there's nothing better than leaving it all to your imagination.
I still feel it's the best of Kneale's feature length stories, even if it's not quite up there with his best shorts or his real masterpiece, the television version of Quatermass and the Pit.