What is a giallo, and why should you watch one? io9 has previously covered that question in detail, but the quick answer is: these vintage European, horror-adjacent thrillers deliver style and sleaze in equal measures. Looking for coherent plots and capable acting? Keep it moving. But for lurid good times that very much reflect the era in which they were made, these Shudder titles have you covered.
Also, as a side note, the horror streamer—which offers many more giallo films beyond just this list, in case you get hooked—also has a 2019 documentary you can watch for a crash course in the genre: All the Colors of Giallo. Stream on Shudder here.