Four years ago, I watched an airplane full of people die horrifically when a terrorist released a toxin into the cabin that caused flesh to disintegrate. Since then, an ad-hoc team—a stoic FBI agent, a wounded scientific genius, and his brooding, polymath son—has investigated similar events through multiple universes and timelines, not to mention untold shootouts and other mortal crises. Tonight, they will determine the fate of our species in its battle with time-traveling invaders in 2036 by attempting to transport a genetically engineered child to a historically important moment in February 2167. And whether Olivia Dunham, Walter Bishop, Peter Bishop and their allies succeed or fail in saving the future, I and many others will miss them terribly.

Fringe was just one of many long-game sci-fi series launched in the wake of the wild success of Lost. That it shared a creator, J.J. Abrams, with that series, only made its middling ratings and muted critical praise more disappointing. But in the face of cancellation fears after a third-season move to the so-called “Friday Night Death Slot,” a solid core of fans organized on social media to advocate for more seasons, and by all indications, Fox executives actually listened. And good that they did, because the show deserved the love of its fans and a chance to spin out its tale–Fringe is the last of those Lost-influenced series, but it was always the best of them all.

A strong source of Fringe’s appeal has to do with the heady structural mix that Abrams and his co-creators, Alex Kurtzman and Roberto Orci, cooked up for the show. Part procedural, part X-Files-like Mystery of the Week (especially in the early seasons), Fringe benefited from the engrossing cadence of the former and the addictive catharsis of the latter. Plus, Fringe’s overarching mythology was rich enough to get lost in, yet controlled, limited, and familiar enough (unlike Lost) that it didn’t veer into the frustratingly arbitrary or absurd. While the show had no problem crisscrossing dimensions, hacking the genome, and resetting time, the most powerful forces at play were far more mundane: corporate and governmental bureaucracy, the difficult relationship between parent and child, pesky human universals like hubris and revenge, regret and love.

The tethering presence of these simple themes has allowed Fringe to test the limits of multiseason television storytelling, as well as viewers’ attention spans. While Season 3 episodes toggled between two parallel universes populated by doppelganger characters, Season 4 abandoned the previous timeline entirely, initially leaving only Peter Bishop with the memories of the previous three seasons. And of course, the fifth and final season has been set a few decades in the future, where society is under siege by super-evolved, pasty humanoids called the Observers from hundreds of years hence. Confusing? Sure, but because so much of the show’s core drama is emotional, even late-comers should find something to latch onto (at least that was the idea), whether it’s Peter and Olivia’s frustrated romance or Walter’s ongoing adventures with hallucinogenics.

That being said, some quotient of science-love is definitely required to appreciate the show. As the literal listing of “fringe” science topics—teleportation, dark matter, precognition, the singularity—in the opening titles demonstrates, this is a sci-fi show that actually engages with real ideas. Fringe daydreams on the edge of current research, often darkly, to fantastic effect. And Fringe portrays the slapdash, MacGyver-esque, aluminum-foil-around-the-particle-accelerator reality of how a lot of real science gets done. In many ways, the show is a gushy love letter to the exciting promise of scientific research, even as it imagines what the limits of such research—and the consequences of breaching those limits—might be.

Admittedly, Fringe has, on occasion, slipped from this critical mood into the trite pieties of good vs. evil, the power of love to overcome bad stuff, etc., but luckily, the show’s penchant for geekery and gaggy humor generally tempered those impulses. Fringe was rife with puzzles and Easter eggs for the devoted, including the mysterious recurring glyphs (the leaf, apple, seahorse, etc.) and the delightful historical inconsistencies between the parallel universes—dirigibles are still in regular use “over there” because the Hindenburg disaster never happened. One of my favorite moments was in Season 2, when we visited Walter and Peter back in the 1980s; the opening titles were adjusted for the occasion, featuring cutting-edge stuff like “personal computers” and “laser surgery,” as well as a new version of the theme song heavy on the Casio keyboards.

In the end, the tender affection fans felt for Fringe gets at why the show is the best sci-fi offering of the past decade or so. Fringe isn’t so much a sci-fi program as it is a program about the beauty and terror and infinite promise of science. Abrams and his team took the whole of the sci-fi canon—indeed, the very idea of sci-fi—as their subject matter in Fringe, which freed the show to revel in the pleasures and problems of the genre—the stuff we really love about it—without being overly tied to a specific issue like artificial intelligence, alien malevolence or wormhole space travel. Battlestar, as excellent as it was, was limited imaginatively by its Cylons, just as the later Stargate franchise ultimately exhausted its interstellar highway conceit. Meanwhile, Fringe has been from one corner of the multiverse to the other, and still feels fresh as it did in that first, flesh-melting flight.

Indeed, but for the shackles of network television ratings—which killed promising entries like Terminator: The Sarah Connor Chronicles, Dollhouse, Heroes, The Event, and the rest of its post-Lost brethren—Fringe could probably go on forever, probing the outer membranes of human knowledge and sometimes pushing right through into lands both gorgeous and terrible. But, as Walter said in last week’s penultimate episode, “It’s been quite a journey,” and all journeys must come to an end. I will be there tonight when humanity takes on the Observers in the battle royale of all time (literally), hoping that messy curiosity wins out over calculated control, and also that the fighting doesn’t create a black hole that converts all of a reality into a cartoon—but in Fringe, anything is possible.