It's not bad for what it is, an Edgar Wallace-period set of psychological crime stories + weird tales. The psychology looks a little quaint now, as I daresay Ruth Rendell's psychological thrillers will in future. Not that I care for those either: they always seem terribly unlikely to me, just as Iris Murdoch characters seem terribly unlikely.
But 30's stories do suffer from this air of 'Ohhh shiny!' when dealing with the new and wonderful field of psychology ie human emotions as quantifiable things. A couple of the stories here have much more faith in the power of suggestion than I can muster; no, sorry, possibly you can scare a sensitive person to death but I don't think you can turn a placid person into a murderer by dropping hints at them.
Rampo goes back to his American namesake for the general tenor of his themes: somnambulist killers (but is he?), murderous twins, the demonic power of mirrors. Again, OK but. Possibly those stories work better in Japanese. I think one of the things a translator should do is make the source sound as plausible in English as it does in its native language, even at the cost of mistranslating and omitting: but a lot of translators prefer to be true to the source. The result is that the writer looks like an idiot. (One example being the way Japanese dispenses with subjects. Narrative English doesn't and mustn't, but some translators think they can get away with keeping the elision in dialogue. Usually they're wrong.)
Again, when you're pulling the 'unspeakable and demonic' trope (and Rampo does) the language of the whole story better be over-heated and baroque enough to support it; if only the last paragraph sounds like Lovecraft, well, the story sounds silly.
I seem to be coming around here to the notion that the translator should be trying to produce a story that works in English more than one that renders the original words accurately. Normally I hate that idea: it's the thinking that results in Japanese anime characters with American names. But still... when a construction that's perfectly normal in one language is weird in the target language, I think it better to be left out. Don't translate o-nee-san as Sis, basically. (The subtitles of The Makioka Sisters sensibly had the husband of the second sister addressing the oldest sister's husband by name, as he would in English; the actor of course was saying o-nii-san.)
Of course then there's the question of whether something that's really genuinely weird tales and scary to a Japanese is going to be anything of the sort to a westerner. Rampo at least seems to have started with a half-western approach anyway, like Souseki. (I like Souseki because a lot of the time he seems to be trying to write English novels in Japanese. At least I think that's the reason he's the most accessible Japanese author I know, while everyone else is opaque and what-the-fuck? Of course, by that argument Henry James was writing Japanese novels in English, and I know he wasn't because the authors he imitates hadn't been born when he wrote.)
But returning to our sheep: another problem is that Asian weird tales and ghost stories aren't scary to me. I was all chuffed when I found an online translation of Tales of the Eastern Studio because now I could read those wonderful eerie Chinese ghost stories. Except they aren't eerie at all. They're the most domestic thing one could think of. Fox spirits not only become human women and have your kids, they arrange for you to have concubines to have your kids as well. How terribly... civil of them.
What makes western ghosts so terrifying to me is that an atmosphere of malignancy hangs about them, even when they do nothing more than moan and cause cold patches. It's not merely that they're inimical to the living, it's that they're so far gone that half the time they don't know they're doing it. They aren't rational; you can't ask them what they want; there isn't even a cause and effect as there is with vindictive Japanese ghosts. 'He did this so now her spirit is doing that.' You can pacify a ghost like that: an apology usually works. But western ghosts-- no way. They can't even hear you. And that's /scary/.