The CW just wrapped up what looks to be an annual tradition, as all four Arrowverse shows joined forces for a massive crossover called "Crisis on Earth-X." While not a perfect crossover by any means, "Crisis on Earth-X" offered a massive dose of superhero fun and a surprising amount of drama for good measure. And ultimately, "Crisis on Earth-X" set a higher standard for what these crossovers can achieve than last year's "Invasion!"

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"Crisis" already had one big advantage out of the gate that "Invasion!" lacked last year - the scope was bigger. All four shows were equal participants in the crossover, whereas Supergirl only briefly connected to the events of "Invasion!". But that's not the true reason "Crisis on Earth-X" was more successful. This year's crossover succeeded because it found ways to meaningfully impact the casts of all four series. It's hard to argue that the events of "Invasion!" had much lasting impact on the heroes of the Arrowverse. But with "Crisis on Earth-X," it's impossible to ignore the ramifications on several key players."Crisis on Earth-X" spoilers continue below! Read our reviews of the Supergirl The Flash and Legends of Tomorrow episodes of the crossover.

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The most obvious fallout of this year's crossover is the death of Martin Stein. Legends of Tomorrow had been building towards Stein's departure for weeks, ever since news broke that actor Victor Garber was leaving the series to focus on a new stage production. The writers could easily have kept Stein's departure confined to Legends itself. But by saving it for the crossover, and by choosing to sacrifice Stein via a heroic death than simply allowing him to retire, they ensured that the conflict between our heroes and the villains of Earth-X had real stakes. Everyone emerged from the battle with the Dominators more or less unscathed, but the same wasn't true for this fight.Stein is a character with ties extending all across the Arrowverse. He may have been a member of the Legends from the beginning, but he started out as a supporting player on The Flash. He even has ties to Supergirl thanks to last season's musical episode. In hindsight, it seems only fitting that the crossover was used to allow the entire Arrowverse to give this character the farewell he deserved.There were other major ramifications to be had in these four episodes. Not only did Barry and Iris finally tie the knot after several seasons of "will they, won't they?", but Ollie and Felicity followed in their footsteps. Both developments promise to have a profound impact on their respective shows. So much of the character drama in the Arrowverse is fueled by romantic entanglement. Much like the comic book source material, it seems as though these heroes are never allowed to find permanent, lasting, stable romance. These weddings promise to have major effects on the universe going forward, especially in the case of the unexpected Ollie/Felicity marriage. Is it truly "happily ever after" for these two, or is Felicity merely opening herself up to new problems by marrying a man who's about to go on trial for his vigilante crimes?For Team Flash, even more significant than Barry and Iris' marriage is the return of Eobard Thawne. This crossover could easily have gotten away with introducing an alternate universe version of Reverse-Flash and killing him off alongside Overgirl and Dark Archer. Instead, the writers specifically resurrected the man that ruined Barry's life and set him down the path to becoming the Flash. The final episode ended with Thawne slinking away to lick his wounds and plot his next move. No doubt that act of mercy is going to come back to haunt Barry down the road. We don't know if The Flash can or will attempt to use Thawne as a season-long villain again, but there's surely more Reverse-Flash-driven conflict headed Barry's way.Team Supergirl may not have been quite as profoundly impacted by this crossover as the rest (in part because most of those characters sat out this conflict), but even that show was impacted by the events of "Crisis on Earth-X" in a meaningful way. The writers made an effort to forge closer ties between Alex Danvers and the heroes of Earth-1, specifically by having Alex drunkenly hook up with Sara and deal with the awkward fallout. And while that encounter was mostly played for laughs, it proved critical in terms of furthering Alex's central character arc in Supergirl: Season 3. Only by meeting Sara did Alex finally gain the courage to move forward from her broken relationship with Maggie Sawyer.On top of all this, "Crisis on Earth-X" paved the way for an entirely new branch of the Arrowverse by introducing The Ray and setting the stage for his upcoming animated series. Not too shabby for four episodes.Whatever problems "Crisis on Earth-X" may have had in terms of structure, the crossover helped make the Arrowverse stronger. It ensured that our heroes faced lasting, permanent consequences in their fight with the Nazis of Earth-X, and it set a clear example for future crossovers to follow. As fun as it is to have so many characters under one roof, there have to be real stakes holding these crossovers together.

Jesse is a mild-mannered writer for IGN. Allow him to lend a machete to your intellectual thicket by following @jschedeen on Twitter , or Kicksplode on MyIGN