Soft Cell weren't the originators of this song, new wave, or synth-pop, but their take on Gloria Jones set the stage for a decade of music.
There are certain songs that people think of as defining an era. This distinction is bestowed upon works based on a combination of their sonic makeup, their shaping of subsequent music, and their greater place in culture. If you have to encapsulate the psychedelic late 60s into a single song, for instance, you'd probably go with Jimi Hendrix's "Purple Haze"; for the disco-fueled mid- to late-70s, I'd zone in on Earth, Wind & Fire's "September"; and for what its music and associated visuals have meant to so many, I'd say that the past six years have been defined by Beyoncé's "Formation."
For all the 80s brought to the pop landscape, it's hard to narrow down its essential sound to a single record. For one, do you go with the start of a sonic era (as I did with "Purple Haze") or its peak (akin to "September")? I ended up deciding on a song close to the decade's beginning which, while not in itself the birth of new wave or synth-pop, was certainly a sign of the genre's (or genres') mainstream arrival. What makes the choice all the more interesting is that it's a cover — a fact that is likely unknown by the casual listener, but one that makes examining how its sound shaped an era all the more nuanced. Indeed, Soft Cell's "Tainted Love" is not the original version, but it is a recording that established important musical tropes that penetrated the popular landscape of the 80s and beyond.
"Tainted Love" was first recorded by Gloria Jones back in 1964 and released in 1965. Her original became a surprising favorite in the UK's Northern soul scene of the 70s, to the point that Jones cut another version in 1976. Marc Almond, Soft Cell's singer, came to know and prefer the original release, and he and David Ball began to cover "Tainted Love" in concert. In 1981, Almond and Ball went into the studio, and in less than a week overall, they had their version ready for release.
Compared to Jones' recordings, Soft Cell's version is in a lower key, is slower, and prioritizes electronics in its backing. While the first of those three attributes was likely a choice to fit Almond's voice, the other two are definitely more artistic decisions. Combined, they result in the 1981 version to be both more sensuous through the lengthening of Almond's phrasings and icier as a result of the synth accompaniment. It's a strange combination of attributes to write about together, but in listening to 80s music it's a tandem that's so often heard, and I believe the heartbreak anthems of that era are so emotive because of the contrast those two ideas present. There's a natural removal from the context of love with that sort of instrumentation — the high melodic synth and the beeping tonic sounding above Almond's voice lead the feeling of detachment, a feeling that soon enters on a further level with his lyrics on "the pain you drive into the heart of me."
Yet despite all the lyrical pain and emotional torment the narrator's going through, there's an inherent danceability to "Tainted Love." In a broader sense, I think a lot of 80s songs are dance-friendly because of their straight-ahead percussion that cuts through the rest of the track. Adding to that for Soft Cell's cover is the similarly straightforward rhythm of the main synth line, accented by those big laps before "run away" and "get away." The vocal syncopation above that base rhythm gets people to move a certain way to the song, but at its core it's the beat at the bottom of the song that makes them move in the first place.
tl;dr Danceable, straight-ahead beat + icy synths + lyrics on heartbreak = a microcosm of the 80s, one that still registers decades on, whether in its original form or sample like Rihanna did for "SOS." Soft Cell may not have written "Tainted Love," but in performing and producing it the way they did, they left more of an impact with their version than any other.