In September 2008, Fox introduced Fringe, a science fiction show created by J.J. Abrams and Alex Kurtzman. It's the story of FBI agent Olivia Dunham (Anna Torv), who tries to solve impossible-seeming cases with a strange team that includes Dr. Walter Bishop (John Noble), a brilliant but slightly insane scientist whose specialty is "fringe" or pseudoscience; his equally brilliant son, Peter (Joshua Jackson); assistant Astrid Farnsworth (Jasika Nicole); and poker-faced Colonel Phillip Broyles (Lance Reddick).

Despite rather unremarkable beginnings, Fringe proved itself to be no ordinary mystery or crime-solving show: Over the course of its run, it packed in monsters, time travel, futuristic overlords, and doppelgängers — plus some of the most thoughtful explorations of what it means to be human in recent TV memory.

The perpetually ratings-challenged series somewhat miraculously made it to five seasons; its series finale aired three years ago today. All the episodes are available to stream on Netflix, so here are four reasons you should watch (or rewatch) this weird little gem.

Fringe builds a fascinating and ever-deepening mythology

I'll admit it: The Fringe pilot is not great. Nor are most of the first several episodes, really; the show initially plays like a sci-fi-tinged twist on a garden-variety procedural cop show. But even if you need to skip ahead a bit to stay invested, it's worth sticking with. The intrigue starts to pick up in episode seven with the introduction of David Robert Jones (Jared Harris), a mysterious villain who ends up at the center of the long-term plot arcs that eventually develop, and Fringe eventually crafts a mythology that gets more fascinating and essential by the week.

While the one-off cases often provide some freaky fun, the best parts of the show lay with its exploration of an alternate universe. In the end of season one and beginning of season two, the Fringe team discovers that Olivia has the ability to travel between worlds due to chemical experiments Walter performed on her when she was a child — and that everyone on the team (well, most of them) has their own counterpart on "Earth 2" — which opens up the show to endless possibilities.

This complex, detailed mythology likely contributed to Fringe's ratings struggles, as the series became a bigger challenge for new viewers even as it vastly improved from its early episodes. It contains a wealth of subtle detail, both visual and thematic, that rewards careful and repeat viewing.

But it also features easier-to-spot delights — including the opening credits, which ordinarily featured words and phrases related to the weird science the team so regularly encountered. In later episodes the words and colors would change depending on what universe or time period the episode was set in, serving as both a nifty extra and an exposition-free way to clue in viewers to what they should expect.

Best of all was what the show did when the story traveled back to the 1980s:

If you're extra impatient, you can watch all the different versions of the credits here, but part of the fun is seeing them change and evolve as you work your way through the show.

The cast is stacked with excellent actors

Fringe's core ensemble is uniformly excellent, but the show would be nothing without John Noble's award-worthy performance. As the endlessly complicated Walter, he plays every side of the character — addlepated old man, brilliant scientist, hubris-driven visionary, heartbroken father, cruelly pragmatic leader — perfectly. In Noble's hands, each version of Walter is believably sympathetic and reprehensible in turns.

The rest of the cast is also great, from Reddick (whom many will recognize from The Wire) as the tough yet utterly loyal Broyles to Nicole as the quiet heart of the team to Jackson, displaying his usual charm as a man torn between two worlds. Torv is especially impressive; the differences between the two Olivias (one from each universe) are subtle, but Torv plays them so convincingly it's totally believable that they're two different people who are also quite adept at impersonating each other. (Check out this unfortunately un-embeddable clip to see what I mean.)

And that doesn't even touch on the stacked roster of guest stars and supporting characters who appear on the series throughout its run: series regular Blair Brown as the ambiguously allied Nina Sharp, Stephen Root as a grieving widower in season four, Leonard Nimoy(!) as Walter's longtime frenemy William Bell, and so many others.

It's great fun to watch the actors stretch their skills once the other universe is introduced; they get to explore the minute shades of their various characters, while the show smartly leaves itself some space to bring back fan favorites even in the event of an untimely death.

The series expertly juggles humor, horror, and heartbreak

Fringe's loose case-of-the-week format gave its writers a lot of leeway, and they made the most of it. Starting with the pilot, which features a plane full of people succumbing to a toxin that basically turns them into Sen. Kelly from X-Men, Fringe routinely turned out creative maladies and supremely creepy visuals. Perhaps the best example is the season three episode "Marionette," in which a depraved (but loving!) man tries to collect all the donated organs from the woman he loved, who killed herself, in order to stitch her back together:

Beyond the horror trappings, each episode tackles a different unexplained occurrence that usually boils down to someone with impossible abilities trying to restore the balance in his or her world. Themes of loss and regret factor heavily throughout the show, as does the idea that everything has a cost. That's why the Olivia of one Earth, for example, enjoys a loving relationship with her sister and niece but has lost her parents, while her counterpart still has her mother but lost her sister to childbirth.

Sound like a huge downer? I promise it's not! Fringe is frequently very funny, largely thanks to crackpot Walter and his insatiable appetite for junk food and drugs. This is, after all, a series that in the pilot introduces a cow named Gene who remains part of the show for nearly its entire run, and frequently features science experiments that hinge on one or more members of the Fringe team ingesting large quantities of LSD.

Plus, there were all kinds of commonplace, unexplained differences between the two universes, parceled out gradually over may episodes: Earth 2 doesn't have coffee, uses blimps as a main mode of transportation, and headquarters its Department of Defense under the Statue of Liberty, for some reason! This adds thrilling, gorgeous color to the often all-too-brief glimpses we get of the "other side," and makes it impossible not to invest in the characters who are so like the ones we've spent so much time with, yet also so exotic.

Above all, Fringe tries to tackle the thorny questions of humanity

Despite all the bizarre pseudoscientific jargon and occasionally gimmicky episodes, the entirety of Fringe really comes down to one question: What makes us us? Every strange instance the team investigates, every new world they encounter in some way relates to the line that separates human from beast, and the reality that the choices we make — whether large or small — gently and imperceptibly accumulate over the days and months and years to shape us into the people we are.

It's a question all of us have asked ourselves at least once: What if I had gone left instead of right? What if I had said yes instead of no, or no instead of yes? If I'd chosen differently, who would I be now?

In the Fringe universe, those questions are answered, but only partially. Though the series spans the past and present and future, and even alternate universes, its characters still don't have all the answers. They still suffer pain and loss and uncertainty. The question, Fringe seems to insist, is not, Who would I have been if...? but instead, Where do I go from here? And in that, most of all, Fringe shows its humanity.

All five seasons of Fringe are available on Netflix.

Correction: The Fringe series finale was three years ago.