I'm going against the grain with this one, as the consensus seems to be that it's an exemplary piece of fifties horror while I find it just pretty good and not lacking flaws. It's fine and fun, but I wouldn't cite it as the Ultimate in genre film for this era.
One big stumbling block for me is that BLACK PIT is suffused in religion. Weird fifties hyperCatholicism touches everything in what is essentially a tweak of the Frankenstein tale: Drs. Aldama and Masali agree that whichever of them dies first will find a way to come back so that the other can go to the other world and return in a living body.
Aldama dies first, leaving behind a daughter which he'd earlier abandoned. The daughter ends up at Masali's sanitarium and chaos ensues before Masali learns of the "horrible price to pay" to accomplish his trip to the beyond. This starts slowly, but picks up pace as it throws in all kinds of crazy happenings, from a lab accident to a music box-lulled madwoman. The acting is pretty solid and there's some absolutely gorgeous lighting and cinematography to be seen.
But it kind of ends up feeling like a LEFT BEHIND movie when the movie shoves Roman Popery down your throat. It ain't subtle, either...Dr. M "cannot go" to a little church and says, "If I knew how to pray..." before the narrator reminds us how Paul said we're not supposed to uncover covered things. FRANKENSTEIN obviously had a bit of this man-playing-God business, but it was much more delicate about it.
I can see why the outlandish elements of the plot and the artful design would win hearts, but this just didn't feel like anything I need to revisit. The Jesus stuff is cloying and the slow parts are pretty damn deliberate. It's worth a watch, especially given how many smart people love it, so check it out and make up your own damn mind. See if you can complete the "senseless struggle to break the barrier that separates us from God."