Legion keeps getting better and better.
In Season 1, Legion borrowed the X-Men's general backdrop--there are mutants, they have special abilities, and people generally don't like 'em--to tell a very personal story about mental illness.
In Season 2, things are different. These days, Legion is going all in on its comic book heritage. By weaving together the themes, tropes, and some other, more direct connections to the comics, Legion is finally starting to feel like a real X-Men adventure. Here's why.
1. Protecting a world that hates and fears them
In Legion Season 1, our heroes were concerned with keeping the mutant haven Summerland safe and saving David Haller from the Shadow King. That's a fine goal, but it's a little self-centered. For their sophomore outing, that the team has thrown in with the government-run Division III in order to stop Amahl Farouk and save the world. In other words, David, Syd, Ptolemy, and the rest are no longer mere mutants. Like the X-Men themselves, they're now bona fide superheroes.
2. The future is doomed (probably)
Days of Future Past. Age of Apocalypse. Old Man Logan. The Aksani's Earth-4935. In the X-Men universe, you can't throw a fastball special without hitting some kind of alternate timeline or post-apocalyptic future. In Season 2, Legion is embracing the trope wholeheartedly. David spends the first few episodes hopping through time. A future version of Syd tries to help him prevent doomsday. Heck, future-Syd is even missing a limb. As per X-Men tradition, that's how you know that things get bad.
3. A couple of honest-to-goodness supervillains
In Season 1, the Shadow King was less a character and more a force of nature. He wore other people's faces and lurked in the corners of David Haller's mind. In Season 2, Amahl Farouk's in all of his glory, and it turns out that he fits right in among Magneto, Mr. Sinister, Apocalypse, and all of the X-Men's other big bads. Farouk's not the only supervillain on the scene this season, either; future-Syd warns David that someone even worse is coming. If it turns out to be David himself? Well, as they say, like father, like son.
4. Young pretty people in love (and trouble)
Many die-hard X-fans start reading for the superheroics, but it's the franchise's soap opera-style twists that keep them sticking around. Between David's missing year, his many secrets, and his devotion to two different versions of the same woman, Syd and David's relationship is getting more and more complicated, and it's not necessarily going to end well. Just ask Kitty Pryde and Colossus, Rogue and Gambit, Cyclops and Jean Grey, Cyclops and Emma Frost, Cyclops and Madelyne Pryor, Cyclops and--eh, you get the idea.
5. We are not alone
When the team's resident scientist, Cary Loudermilk, is analyzing the sphere that kidnapped David during the Season 1 finale, he name drops the Shi'ar. In terms of Legion, that doesn't mean much. In terms of the X-Men, that means everything. In the comics, the Shi'ar are an alien race who play a major role in the X-Men's adventures (Professor X and Shi'ar Majestrix Lilandra might be the X-Men's OTP), especially the classic Dark Phoenix Saga. The Shi'ar may or may not have much to do with Legion's overall plot, but just knowing that they're around brings Legion much, much deeper into the X-Men's world.
6. Professor X, up to no good once again
In "Chapter 11," the third episode of Legion's second season, the Shadow King calls out David's father, Professor X, and accuses the X-Men founder of interfering in other people's business. For Chuck Xavier, that's pretty much par for the course. Over the X-Men's 55 year history, Professor X has gotten up to all kinds of shady stuff, including crushing on his teenage student, faking his death to teach his teen charges a lesson, enslaving a sentient artificial intelligence, concocting plans to kill the X-Men, and much, much more. It's not just a Legion thing. That guy is seriously the worst.
7. Other mutants are having other adventures, we're just not seeing them
During the season's first episode, Ptonomy casually mentions something called the Lazarus Affair, which many fans are taking as a reference to a relatively obscure storyline from the early '00s. It's a throwaway line, but if the fan theories hold up--and the evidence is stronger than you'd think--it implies that X-Men characters, like Deadpool 2's Domino, are out there doing their own thing. That makes Legion kind of like walking into a comic shop and seeing all of the X-Men books on the shelves. There's no way to follow them all, so you have to follow the storylines you're interested in. Everything else still happens. You just don't know the specifics.
8. Are they people, or are they weapons?
When is it okay to treat a person like a tool of war? The X-Men comics confront that question all the time, and it looks like Legion is going to tackle that issue head on, too. Not only is Division III raising an army of super-soldier children (if you thought of X-23 and the Weapon X project when you learned that, you're not alone) but we recently learned that the Mi-Go monks were taught that Division III has a weapon that can stop the Shadow King. That weapon's name? Why, David Haller, of course. It's not clear exactly what this means for David's future, but if Mr. Haller has questions, he might want to look up a fella named Logan. He's been down this road a few times before.
9. Secondary mutations and newfound abilities
One of the fun things about following the X-Men is that their powers are constantly growing and changing--Iceman used to look like a snowman, and now he's an Omega-class mutant--and Legion's second season is taking that trend and running with it. Now, Syd can swap minds with animals. Cary and Kerry's whole body-sharing mechanic has been flipped. David can travel through freakin' time, even if he needs help from Cary's isolation chamber to do so (and lets not ignore how closely that device resembles daddy Xavier's own psychic-booster, the computer known as Cerebro, either).
10. Scenes from the X-Men comics? Yeah, we've got those
In Season 2's third episode, Legion flashes back to the Shadow King's physical death, and if it looks familiar there's a very good reason. The scene itself is lifted directly from Uncanny X-Men #117, which contains the first battle between Xavier and Amahl Farouk. While Legion's shown us a version of this conflict before, this iteration unfolds exactly like its comic book counterpart, even if the camera never actually shows Professor X.
11. David himself
Here's the thing about David Haller: In the comics, he's not a good guy. Not always, anyway. Legion might've used the Shadow King to explain away David's schizophrenia, but he's headed down a dark path just the same. He's lying to his friends. He's working with the enemy. It's not a matter of if he'll break bad, but when. After all, as Emma Frost, Mesmero, Cassandra Nova, Jean Grey, and David himself prove, in the X-Men's world, psychics are always bad news. Avoid them at all costs.