The 'Brood Saga' (everything's a bloomin' saga now eh) is one of the most successful of Chris Claremont's big X-Men stories. It's tightly paced, full of ideas, with a central threat which forces the kinds of character moments Claremont loves to write, and a dizzying expansion of scope from #162's terrific Wolverine solo showcase to #166's high-concept double issue finale.
But it's never quite had the fan reputation of the other landmark Claremont-era stories. It's overshadowed by the rest of artist Paul Smith's run, by the original Shi'ar story, by later 80s crossovers and events, and obviously by the Dark Phoenix Saga. And it's obvious why: it's the peak of a particular way of doing the X-Men comic that Claremont clearly loved but that fell by the wayside later.
Uncanny X-Men is, on the face of it, a superhero book, and later it got a reputation as one particularly suited to exploring prejudice and the experience of minorities. But Claremont got his start at Marvel in the 1970s, the one time in the company's history when straightforward superhero stories were very much not Marvel's creative heart. In the face of recession and softening newsstand sales, Marvel grabbed onto any fad going: martial arts, kaiju, toy tie-ins, pulp sci-fi, cosmic sci-fi, swords-and-sorcery, political thrillers, horror... sometimes these comics would be integrated into the 'Marvel Universe', sometimes apparently not, but a lot of them were just plain better than the long-underwear book. And collectively they gave an impression of Marvel as a brand where any kind of genre fiction could find a home.
But by the time of the Brood storyline it's 1982, and Marvel is beginning to move a different direction - investing in marketing, starting to draw together its core superhero books, and courting the Direct Market, speciality comic shops whose clientele generally want Marvel to do Marvel Universe stuff. Claremont's X-Men, though, has up to this point been the last great survivor of the magpie Marvel 70s - his vision for the comic is clearly one where (like Doctor Who) the basic concept can be an umbrella to hang any variety of story on.
Since John Byrne left, Claremont's had free rein to treat the X-Men like this. In this and the last volume alone we've seen the X-Men idea used as a springboard for high fantasy (the Arkon stories), traditional horror (Dracula), weird pulp horror (the Belasco issue used to age Magik), thrillers (Xavier and Magneto hunting Nazis), children's picture books (Kitty's Fairy Tale) and of course vast quantities of space opera sci-fi, which is Claremont's default setting when he's got Dave Cockrum on art.
To put it another way, Claremont has been on the book for 70 issues at this point - it's already a historically long run, longer than the X-Men's original lifespan. And about one-sixth of those issues have involved the Shi'Ar Empire or its foes, vastly outnumbering the issues dealing with anti-mutant prejudice. The Brood Saga is the high watermark of this idea that you can use the X-Men to tell any story you want - a heady if blatant mix of ideas from Alien, Star Wars and Anne McCaffrey's Pern novels, with the anchor for readers being simply the fact that this is happening to the characters we've come to love.
The idea of the X-Men as a cross-genre comic never entirely faded - you get sci-fi, epic fantasy, Russian folklore and much more poking its nose into the comics before Claremont leaves, and he had an entire book (Excalibur) where this kind of playfulness was its raison d'etre. But it's never so intensely part of the comic again after 1981-2, and the two issues which bookend the Brood Saga are a big part of why.
The first (#161) is a flashback sequence set in Israel with Professor X meeting Magneto for the first time - and demonstrating atrocious doctor-patient ethics with Gabrielle Haller. Read in sequence the issue - and it's a good issue! - feels like a throwaway. But it lays on the table what's been implicit in the past - Xavier and 'Magnus' as former friends, and two sides of the mutant rights coin. It's almost impossible to exaggerate how foundational this idea - Professor X and Magneto are pursuing the same goal by different means - becomes: it's a more important introduction than any single character Claremont creates and it defines the comic to the present day.
The second (#167) introduces the New Mutants to the X-Men comic, and it's important because of those behind the scenes shifts in Marvel's priorities. Marvel wanted to introduce a second X-Title, Claremont reluctantly agreed if he could keep control over it. The New Mutants is as un-superheroic a book as he could make it, but introducing a new generation of young mutants is a huge shift. It turns ideas like the future of mutants and anti-mutant prejudice from abstractions into story points by making the idea that there are new mutants appearing all the time more tangible.
Taken together these stories rewrite the X-Men's ground rules. The team's mutant identity is suddenly more important than ever, and the divide between their founder and their arch-enemy is now one based on what that identity means and the right way to safeguard it. Together with Days Of Future Past - which shows the consequences of getting it wrong - the comic's new world is in place, and it's a world with increasingly little room for space opera or Dracula.