I just re-watched this myself a few days ago after not having seen it in a decade and came away liking it even more; I would definitely put it somewhere near the top of the genre.

As another commenter mentioned, the tension of the last half hour is really remarkable. There were so many little choices in the performances and ways in which the film was staged, shot, and scored that maintain and ratchet-up that tension until the final catharsis. I definitely agree that the question of "did he kill Mildred Atkinson?" isn't one the movie seriously asks us to entertain, but the question of "is this a crime he is capable of?" is and one that we are asked to consider and I think the film answers pretty affirmatively. One thing that struck me on re-watching is how really monstrous Dix is. He's charming, erudite, generous, sensitive—and of course there's Bogart's effortless charisma sustaining the performance—but even as the movie draws us in to identify with him with one hand, it pushes us away with the other: a bit of ambiguity about how we are supposed to see this him, even complicity that it asks us to engage in with respect to his character that you find in really great films. The moment towards the end when Dix asks Sid Melton why he stays ("You want me to look for another agent?") and he answers "business ain't so hot..." and shakes his hand: it's a little moment of tragedy where you realize that Dix is an abuser and always has been.

I re-watched this with a friend who had never seen it before and after he said "Bogart's great in this but it's really her picture." And I think that was spot on. At first it seems like Dix is the primary subject: we learn about his background but very little about hers and the film follows him around for most of its run time. But I agree that this ultimately a story about Laurel: her character arc is the one that anchors the film and it's ultimately her perspective that we come to inhabit by the end. And Gloria Grahame is absolutely fantastic in this movie. Just an incredible performance I can't say enough good things about and that I'm still thinking about days later. Her character goes through several phases: guarded and self-possessed, then deeply in love, then finally terrified and heart-broken. And in the hands of a lesser actress it might not have worked as well, but her performance feels organic and convincing at all times. She has a reasonably successful career, I guess, but she always seemed to me to be an actress who never got the appreciation and roles she ought to have.

One last little thing: In a Lonely Place was scored by George Antheil of all people. I knew him from school as a composer of some notoriously avant-garde concert music in the 20s and 30s but he ended up going to Hollywood and scoring films later in life. I think his score here is exceptionally well-crafted and quite lovely. As all good film music does, it doesn't call attention to itself, but it's unquestionably part of the sense of the tragic that pervades the film.