The cast of Law & Order, circa 1999. From left, Jerry Orbach, Angie Harmon, Sam Waterston and Jesse L. Martin. (Universal International Television/Getty Images)

The verdict is in: Law & Order is kaput. After 20 seasons and more than 450 episodes, NBC is cancelling the iconic drama. It's an abrupt end for one of the most influential network series of all time.

Law & Order didn't just inspire spinoffs, copycats and any number of crime procedurals. It perfected and franchised a narrative formula.

Adore it or deplore it, you can't deny its impact. This quintessential primetime drama didn't just inspire spinoffs, copycats and any number of crime procedurals. It perfected and franchised a narrative formula, which ran as follows: scene of the crime, wisecrack, investigation, litigation, confession, end credits. It's the kind of easily digested form of entertainment that audiences have come to expect, albeit in increasingly slick packages.

Law & Order debuted on Sept. 13, 1990 — back when Cheers was the number one sitcom on TV and HBO was still basically a pay-per-view specialty channel. The brainchild of Dick Wolf, a veteran TV writer (Hill Street Blues) and producer (Miami Vice), Law & Order fused two classic TV genres: the cop drama and the legal thriller.

Jeremy Sisto as Det. Cyrus Lupo in a scene from a recent Law & Order episode. (Will Hart/NBC/CTV)

Before Law & Order, cops and lawyers mostly kept to their separate spheres, with Perry Mason and Matlock in the courtroom and Hill Street Blues and Cagney and Lacey working the street. Law & Order bridged the gap in the audience's imagination — giving viewers the who, what, where, when, why and what-happened-next of crime and punishment, all in one episode.

Cops got the first half-hour to land their bad guy, passing off the second half to the lawyers to win a conviction or confession — sometimes both. That efficient narrative technique, which felt new, eventually hardened into a convention. Its greatest comfort: you always knew what was coming next. In fact, like the jazzy theme song, you looked forward to it. Ba-bum.

The set-up wasn't its only original feature. Shot in New York City, it was one of the first dramas to really sink its teeth into the Big Apple, worms and all. The locations were real and street signs could be trusted. (Soundstages and back lots were for amateurs.) Law & Order went for an authentic urban feel, drawing on Manhattan's mythical status and ethnic diversity to feed its drama. It also drew from a pool of accomplished New York stage actors, like Philip Seymour Hoffman, Len Cariou and Christine Baranski. New York itself was a major character — in fact, it was one of the only regulars to survive Dick Wolf's frequent cast culls (see sidebar).

Where other dramas borrowed from TV's catalogue of cliché plot lines — the cheating husband, the corrupt heiress — Law & Order often looked outside the medium. The show's "ripped-from-the-headlines" approach to storytelling kept viewers hooked. Whatever scandal, conspiracy, political intrigue or sensational murder was keeping journalists busy usually found its way onto the show, in an embellished form. From the brutal death of six-year-old Lisa Steinberg to the sex life and public misfortunes of former congressmen Gary Condit, real-life tragedies and scandals kept the series afloat and culturally relevant. (Last season, the off-camera drama surrounding TLC's Jon and Kate Plus Eight even inspired an episode.)

Law & Order generated three spinoffs: Law and Order: Special Victims Unit, Law and Order: Criminal Intent, and Law & Order: Trial by Jury. (The latter was cancelled after one season.) SVU is the original show's dirty-minded little brother, focusing exclusively on sex crimes — the more outrageous, the better. (Not surprisingly, it's the most popular spinoff.) Criminal Intent introduced audiences to the Major Case Squad, a division of the NYPD that takes on high-profile murders and crimes. (Bo-ring.) Both spinoffs are faint reflections of their original. They got the formula, but they didn't get the note on novelty. In both shows, the "punishment" section of the Law & Order formula is significantly absent; an excess of sensationalism has replaced it.

Wolf's franchise so dominated both the legal and cop drama genres that it encouraged variation — writers took the formula and added a marketable twist. Instead of cops and lawyers, they sought out lesser-known cogs in the wheels of justice. In 2000, CSI dramatized the work of those who process the evidence, the preternaturally wise crime scene investigators. (CSI Miami and CSI New York followed shortly after.) In 2003, along came Cold Case — meet the cold case investigators! Medium, The Mentalist, Lie to Me — each one of these series are a response to the pattern set down by Law & Order.

Whether it's from the perspective of a psychic or a mentalist, the action still boils down to the basics: crime, wisecracks, investigation, confession and credits. Only the second step — the complicating factor of justice — is absent. The lack of interest in the rule of law, even in Law & Order's spinoffs, isn't odd given their narrative simplicity. The question of justice aside, it's hard not to feel that some of the Law & Order-plus-CSI-meets-Medium innovations border on parody. (I'm still waiting for someone to successfully pitch SCTV's Plain Clothes Mountie to a network.)

Law & Order may be fading to black, but its formula, distilled to a simpler, more sensational form, lives on in any number of procedural dramas. And I don't care how many Who songs the producers of CSI get their hands on, no series can compete with Law & Order's killer theme. Ba-bum.

The final episode of Law & Order airs May 24.