Almost 15 years on, Lost remains one of the most divisive television shows ever, a sci-fi mystery box rich with references, monsters, time travel, and spiritualism. Its mysteries eventually grew beyond its own storytelling capabilities, and the series ultimately suffers for it. But that doesn’t change Lost‘s impact; love it or hate it, it changed network television forever. It also launched the career of Damon Lindelof, who went on to create The Leftovers, one of the greatest television series of all time. Both shows share mystic DNA, filtering stories about higher powers, death, and the meaning of life through a diverse array of damaged characters.

Lost spanned six seasons, and almost every episode packed some kind of grand-scale emotional punch, or a shocking twist in the ever-evolving story of this mysterious island and the plane crash survivors who land there and attempt to understand why. There are plenty of episodes to choose from when making a master list, but here are 12 that defined the language of Lost and made it such a unique and exhilarating television experience.

1. “The Pilot” (SEASON 1, EPISODES 1 & 2)

Contrary to popular belief, J.J. Abrams didn’t have much to do with Lost beyond its initial conception and the pilot episode. But he did give the show its cinematic identity. The first episode is pure pulpy adventure. A plane crashes on a remote Pacific island; a terrifying-enough experience on its own, made worse by their total isolation, a monster stalking the jungle around them, a polar bear, and a radio tower containing a 16-year-old transmission that was never received. The essence of what Lost is and would be is perfectly contained in this two-parter, establishing its large cast, and its larger ambitions.

2. “Walkabout” (SEASON 1, EPISODE 4)

This is the episode that really changed the game, and showed the true specialness of Lost‘s format. Island weirdo John Locke is treated to an off-island flashback that reveals that the hunting guru was actually a paraplegic before the crash. The island has afforded him a second chance, imbuing him with a spiritualistic knowingness his fellow survivors haven’t yet been enlightened to. Lost‘s flashbacks were a core part of its structure, and “Walkabout” showed the power of what they could do.

3. “Do No Harm” (SEASON 1, EPISODE 20)

Early on, Lost earned a reputation for being totally unafraid to off its key cast members. That started with this season one entry, when Boone fell victim to his injuries and island doctor and de facto leader Jack was unable to save him. No one expected Ian Somerhalder, one of the show’s most recognizable faces, to die off so soon, but Lost never cared about pretense. Its body count would only increase after Boone’s passing, though thanks to the island’s mystical properties, the actors usually returned in some fashion later on.

4. “Orientation” (SEASON 2, EPISODE 3)

Season 2 is when Lost‘s modus operandi started to show, and “Orientation” made a lot of suspicions very clear. After the survivors dig up a hatch in the middle of the jungle and enter it, they find an enormous underground bunker containing a man named Desmond, who has been instructed to push a button every 108 minutes. The button-pushing is meant to “save the world,” Desmond tells them. Whatever that means. “Orientation” also properly introduces us to the Dharma Initiative, a team of scientists who studied the island until a mysterious “incident” derailed their work. “Orientation” sets the mood for the next chapter of Lost, offering up enough answers to satiate, but enough question to keep us pressing on.

5. “The Other 48 Days” (SEASON 2, EPISODE 7)

At different points in its run, Lost would introduce a new set of characters on the island, an attempt to keep the show fresh, and to give us new people to connect with. This episode revealed the survivors of the tail-end of the plane, who crashed on a different part of the island. Both sides thought the others were all dead, and spent 48 days in brutal conditions – the tail-enders especially. “The Other 48 Days” introduces a lot of characters who end up dying and not mattering much, Michelle Rodriguez’s Ana Lucia specifically, but it set up a formula that would be deployed better later on, with the introduction of Ben and Juliet, and the freighter folk in Season 4.

6. “Exposé” (SEASON 3, EPISODE 14)

This is a controversial pick, but let’s be clear: “Exposé made it clear that Lost‘s creators were in on the joke. The show took some heat early on on Season 3 for attempting to backtrack and tell stories about the less-important survivors. That idea didn’t gel well with audiences, who saw it as a distraction, and so midway through the season they killed these characters off in a fantastically over-the-top, winking fashion. Nikki and Paulo were always boring and tertiary, so the flashback made them ridiculous diamond-stealing criminals, and the island story saw them bit by a paralyzing spider and buried alive by the main survivors who can’t stop asking “who are these guys again?” Lost loved to let you know when it was being self-aware and copping to its mistakes. “Exposé” is its most gleefully unnecessary episode, and we love it for that.

7. “Through the Looking Glass” (SEASON 3, EPISODES 22 & 23)

Midway through its run, Lost completely flipped the script. Those flashbacks you thought were so secure? How about we introduce flash-forwards, and don’t tell you that what you’re seeing is the future until a balls-out coda in our third season finale? That’s exactly what Lost did, pulling the rug to reveal that the disheveled off-island Jack scenes were actually Jack of the future; he was rescued, along with Kate, who pops up in the final moments to completely melt our brains into goo. How did they get off? What happened to everyone else? Has there ever been a TV mind-fuck so utterly epic? Luckily, the on-island story was equally compelling, though totally devastating, and ties back to the flash-forward reveal: Charlie sacrifices himself to save Desmond and let him know that the boat they believe is on its way to rescue them is actually full of traitors. His death and the flash-forwards re-energized the show and opened up a whole new world of storytelling possibilities.

8. “The Constant” (SEASON 4, EPISODE 5)

Every Desmond-centric episode of Lost is important, but this Season 4 output is its most successful, and arguably the series’ best-ever work. It distills everything that’s great about Lost; a sci-fi element telling a very human story that is mostly contained but also edges the story forward. In this case, we see Desmond, his consciousness bouncing through time, who is reoriented when he’s able to speak on the phone to his long-lost love, Penny. Their conversation is one of the show’s most beautiful moments, bombastically emotional but for all the right reasons.

9. “La Fleur” (SEASON 5, EPISODE 8)

Lost got heavy into time travel in Season 5, testing the waters of how totally weird this show could be. It had a lot of fun with the concept, which was best-utilized in this Sawyer-centric episode. Sawyer was always a popular character, but seeing him take on a leadership role in the “past” – which was, thanks to time travel, his future – was a real treat. It made the whacky stuff feel grounded, and centralized new dynamics in the cast, including Sawyer’s relationship with Juliet, which blossomed into romance.

10. “The Incident” (SEASON 5, EPISODE 16 & 17)

Like “Through the Looking Glass,” the Season 5 finale once again completely re-arranged the show’s formula. We’re introduced to the mysterious and ancient Jacob and Man in Black in the episode’s opener, and then we witness the “incident” hinted at since Season 2. During the detonation of an atomic bomb, Juliet implodes in an attempt to reset time. The episode ends with her sacrifice and a flash to white, setting in place the flash-sideways concept of Season 6.

11. “Ab Aeterno” (SEASON 6, EPISODE 9)

Lost flashed into the deep past a few times in the final seasons, but never so effectively as it did here with Richard. He first popped up in Season 3 in a shroud of mystery, and his origins are finally revealed here in a flashback that doesn’t make a whole lot of sense. However, the episode fully illustrates that when Lost is at its peak, realism doesn’t matter. Richard’s story, like Desmond’s in “The Constant,” is grounded in love. He’s the island’s oldest inhabitant after Jacob, an ageless relic of a mystic order he’s pledged to and can’t escape.

12. “The End” (SEASON 6, EPISODE 17 & 18)

A lot of your devotion to Lost will depend on how you feel about its finale. Many hate it for not offering up the answers they expected, while others are able to connect to its character-driven message: the people who change our lives are more important than the celestial answers we seek. It’s a hard swallow for a show that was all about set up and very little about payoff. But if you can get past that, the beauty of the finale can sink its hooks. Lost, for all of its brazen weirdness, was ultimately a show about accepting people, and yourself. (And no, they weren’t dead the whole time.)

Images: ABC

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