At the time, the fact that the series focused on procedure was revelatory. Even fans would grow attached to certain regular characters more than others (Sam Watterson's D.A. Jack McCoy and Jerry Orbach's Detective Lenny Brisco are generally considered to be the "mascots" of the series), and the series remained fairly consistent throughout its impressive 20 season run. There was some evolution over time; the earlier 90s seasons being "grittier" in the cop sections (good "average" New Yorkers under assault by psychos, gangsters and "ghetto" thugs) and preoccupied with villainous defense attorneys and the O.J./Menendez-era boogeymen like "race card" and "psychobabble" defenses. Later seasons would gradually change course, leading to more socially/politically nuanced stories which often found Watterson's McCoy - a onetime leftist-radical turned fight-for-the-little-guy legal legend - using legalistic-loopholes of his own to bring the hammer of law down on neo-nazis, homophobes and other 21st Century villains.
Fans were shocked when the series was cancelled one season shy of tying the record (for number of seasons) held by Gunsmoke, but lately there's been talk of reviving the series with an "all-star lineup" of earlier characters has begun to gain traction.
LAW & ORDER: SPECIAL VICTIMS UNIT (1999 - Present)
What is the (for now) sole surviving L&O was initially pitched as a "soapier" cousin to the original: Greater focus on the characters and built around a special police unit (operating under the supervision of a single prosecutor) dedicated exclusively to sex crimes. In the first season, there's a pretense toward using that particular specialization as a venue for advocating on behalf of victims and the basic idea of treating rape, harassment and abuse allegations as serious crimes; but inevitably that gave way to being an excuse for lurid, sleazy or even darkly-titilating storylines that had always proved to be the original series' most reliable eyeball-catchers ("High School Prostitution Ring! Killer Dominatrix!! Lesbian Stalkers!!!")
The show got perpetually more ridiculous as it went on, but that proved to be a strength buoyed by a reliably excellent ensemble cast. Mariska Hargitay and Christopher Meloni were the main detectives, Olivia Benson and Elliot Stabler, effectively Dirty Harry split into partners differentiated mainly by gender and the rationales by which they justified pounding perverts and sleazebags into hamburger: him the generically-conservative, guilt-powered Catholic family-man with a military background and a black-and-white moral code, her the patriarchy-punching Amazon gunslinger culling vengeance for raped women and abused children across the city. Onhand for gallows humor was Richard Belzer as John Munch (a character migrated to the series from both Homocide: Life on The Streets and The Wire) and, eventually, Ice T as streetwise Tutuola.
SVU deliberately avoided the rigid formula of the original series, tipping focus to the cops (especially as Benson and Stabler became audience favorites) and letting cases play out accordingly. Eventually, even the sex-crimes focus became malleable: It's pretty standard now for an episode to open with a sex crime only to make it the "gateway" to the "real" story; like in "Wildlife," where the discovery of a dead woman who looks like she might have been sexually-assaulted is an excuse for SVU to clash with Russian exotic-animal poachers who are trying to smuggle a rare endangered monkey into the country (it's in a basketball - really) for wealthy Chinese gangsters who want to turn its bones into expensive chopsticks.
By now, a lot of the "prime years" cast has departed, leaving Hargitay's Benson as the centerpiece of the series and indeed the "face" of the franchise at this point.