Adjectiveless X-Men is the fan term for various X-Men series, so-called because... well, there's a lot of X-Men books, and adding "adjectiveless" helps make the distinction. Anyway, this page will refer to issues 1-113 of X-Men as volume 1 and issues 157-207 as volume 2.
While the X-Men debuted in a series called The X-Men, that book was retitled Uncanny X-Men and is referred to as such. By 1990, there were three X-titles, the original, X-Factor and New Mutants (well, four if you include Wolverine). Because of the huge cast, a second central X-Men title was announced, written by Chris Claremont and drawn by new superstar Jim Lee. Issue #1 was released in 1991, and is still the best-selling single issue of all time. This split the X-Men into two teams: the blue team (in Uncanny X-Men) and the gold team (in X-Men). This series is known for its bevvy of crossovers, which also means it's very difficult to collect in trade.
In 2001, the series was retitled New X-Men for Grant Morrison's cerebral sci-fi run (not to be confused with New X-Men: Academy X, the third volume of New Mutants), before reverting back to X-Men. That series eventually retitled itself X-Men: Legacy, which initially focused on continuity-heavy stories featuring Professor Xavier before shifting focus for the remainder of its issues to Rogue. It too is a part of numerous crossovers. For convenience, many generally refer to the entire series, bar the New X-Men run, as X-Men: Legacy... Comic books are confusing.
A second Adjectiveless X-Men series was launched in 2010. This series focused on the role of the X-Men in the wider Marvel Universe, and featured "guest characters" who usually don't appear in X-books, such as Blade and Daredevil. This series was eventually canceled, and replaced by its successor, another Adjectiveless series. This series was launched with the Marvel NOW! initiative, and features an all-female team. While Uncanny X-Men, Wolverine and the X-Men and All-New X-Men focus on Cyclops' team of rebel X-Men, Wolverine's school, and the original time-displaced X-Men, respectively, and the X-Force titles are their own little thing showcasing mutant black ops teams, this series just features an X-team in general. It's become known as "that other X-book" due to being largely influenced by the other X-books. Its second story arc was a crossover, and two of its cast were hijacked by other series. This series crossed over with the other X-titles in the Battle of the Atom Bat Family Crossover.
A third Adjectiveless X-Men series will launch in 2019, written by Jonathan Hickman as the main ongoing for the X-Men line of comics. It is part of the Dawn of X relaunch. For more on that, see Jonathan Hickman's X-Men.
Tropes applying to Volumes 1 and 2:
- Anti-Hero: Bishop, of the '90s Anti-Hero variety when he first appeared, being a police officer from a Bad Future with a fondness for using guns rather than his mutant powers.
- Brainwashed and Crazy: For Claremont's swan-song on his first seventeen year run on X-Men, he brought this trope along one last time, with half the time getting brainwashed into following Magneto.
- Breaking the Fellowship: The pre-Messiah Complex team, thanks to Mystique and Lady Mastermind's betrayal. As Cyclops bluntly points out to Bobby, there's no point pretending the team even exists when of their members two have turned traitor, one's possessed by Malice (Karima), another's captive (Rogue), and Cannonball's hospitalized thanks to Sinister.
- Chuck Cunningham Syndrome: Peter Milligan's run had Mystique repeatedly trying to set Rogue up with Pulse, a mutant who could deactivate the powers of anyone near him. The very issue Milligan left, Pulse vanished like he'd never existed, and was never mentioned again.
- Eyes Always Shut: The series launched in the 1990s, so Youngblood's Disease was common in the early years.
- Eye Scream: Blindfold, in the last issue of "Blinded by the Light", thanks to foreseeing Hope's birth, which makes her start bleeding from underneath her blindfold. All the more alarming because Blindfold doesn't have eyes.
- Foreshadowing: When attacking Cable in issue 200, Gambit asks him if he knows the phrase "two minutes 'till dawn". Several issues later, Cable repeats it to baby Hope.
- It's Personal: Sebastian Shaw, in the Cronus Machine arc of Legacy, which is the only reason he's involved at all. Up until he learnt he was threatened, he'd not cared much beyond "vague curiosity".
- Loads and Loads of Characters: So much that the team was split into gold and blue teams.
- Make Way for the New Villains:
- Magneto's death in issue 3 was supposed to be him getting Killed Off for Real, in favor of folk like Fabien Cortez.
- Almost immediately after Claremont left the Hellions, long-standing rivals to the New Mutants, were slaughtered almost to a man to make the Upstarts look dangerous, in what is generally held as one of the most mean-spirited uses of this trope ever.
- My Skull Runneth Over: Rogue, just before Messiah Complex, thanks to an ancient alien weapon that absorbs the minds of anyone it comes near, and has been traveling across galaxies for centuries.
- No Good Deed Goes Unpunished: Sunfire, during "The Blood of Apocalypse", risks his life to crawl back through Apocalypse's base to save Gazer from becoming a Horseman... only to find Gazer is no more, and so Sunfire gets made a horseman himself.
- The Purge: Issue 200 through 204 has the Marauders going around finding anyone with time-travel abilities or knowledge of the future, as part of Sinister's scheme. Blindfold's the only one to get out, thanks to seeing it coming.
- Reforged into a Minion: Happens to Sunfire, Polaris and Gambit during "Blood of Apocalypse", each becoming a Horseman. Gambit actually did so willingly, but he'd been planning to turn it against Apocalypse, only for the brainwashing to prove far too strong.
- Sexy Surfacing Shot: In Issue #8, Scott catches sigh of Psylocke rising out of the water in her leotard and starts stuttering causing Jean to get extremely jealous.
- The Bus Came Back: Karima Sharpandar returns during Mike Carrey's run, having last been seen in Chris Claremont's Excalibur a few years before.
- Token Evil Teammate: Rogue's team had half its team be token evil folk - Mystique, Sabretooth and Lady Mastermind. It was honestly astounding it took as long as it did for everything to go to crap.
Tropes applying to Volume 3:
- Guest-Star Party Member: Daredevil, Blade, the Future Foundation, Spider-Man, Ghost Rider and War Machine.
- Superman Stays Out of Gotham: The entire point if the series was to avert this and have the X-Men combat threats in the Marvel Universe as a whole.
Tropes applying to Volume 4:
- Back from the Dead: Madelyne Pryor. Downplayed with Selene Gallio, who is instead just reassembled from being dispersed into the atmosphere.
- The Big Guy: Rogue acted as this for the brief time in which she was present. Monet fills her shoes after she left.
- Bumbling Mom: Jubilee isn't a very responsible parent, taking almost every opportunity to ditch Shogo onto someone else, even if those people are in no way qualified to babysit (O5 Iceman and Beast).
- Dating Catwoman: John Sublime returns and gets some Ship Tease with Rachel.
- Evil Counterpart: The Sisterhood of Mutants is one to the book's feature team, being an all-female team and all.
- Mama Bear: The entire team acts as this to Shogo.
- The Smart Guy: Kitty Pryde, who left the team.