Ok, a quick rundown on the storylines to remind folks, so of course..
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+Days of Future Past - 2 issue series, a wolrd where the humans win. Sentinels slowly kill of the remaning outlaw X-Men as new President Kelly ordered. Classic Chris Cleremont & John Byrne.+Dark Phoenix Saga: Most folks know this one from the cartoon: Jean Grey is taken over by the godlike entity of the Phoenix, features such highlights as an X-Men war vs Shi'ar empire, Wolverine alone bailin out the team, and finally, Jean Grey's sacrficie...this one'd win in most corners.
+Mutant Massacre: The underground Morlocks are slaughtered by Mr Sinister's band of Sabretooh & his killers; the X-Men are forced to kill in retaliation. Great Wolvy/Sabertooth fight, Angel loses his wings, etc.
+Inferno: hell on earth, Madelyn Pryor, goblins, etc - i never finished this one.
+X-Cutioner's Song: Maassive battle of X-Teams vs Stryfe...id hype it more if i managed to read it, sorry. :embarrassed:
+Fatal Attractions: Xavier's all out war against Magneto: Collosus defects, Wolvy loses his adamantium, and folks die. This one was great, spread out across all X-books that month with gatefold covers & great holograms on em. Art by Jim Lee.
+Age of Apocalypse: Xavier is killed before the X-men come about, its the opposite story of "Days of Future Past", where the mutants rule and all humans in America are slaughtered by Apocalypse. Its a great "What If' series, my vote prolly goes here to be honest. Written by Mark Waid of Kingdom Come, art by Adam Kubert.
+Onslaught: Xavier betrays the team, and it takes the entire Marvel universe to take him down. Badass stuff, also by Mark Waid, but hard to read, as it spread out across the entire marvel universe that summer.
+E is for Extinction: First series of the New X-Men book, Cassandra Nova is introduced & begins her complete deconstruction of the X-Men, i cant say enough good bout this one. Grant Morrisson (JLA, Invisibles) and Frank Quitely on art, who i still kinda dont like.
+The Tomorrow People: 1st arc in Ultimate X-Men: see Cyclops defect, another grand Magneto/Xavier battle, and a lot of new twists on it, all to the art of Andy Kubert, with Mark Millar at the helm.
Other possible arcs i had no room for are X-Tinction Agenda (i didnt read it, either), The Phalanx Covenant (which introduced Generation X), The Magneto Wars (it wasnt that good), Operation: Zero Tolerance (it really wasnt very good), Weapon X (2nd arc in Ultimate X-Men), and the current runnin line in New X-Men, which isnt over yet so i cant really put it up here. There's plenty here, some of which i think a few of us have read, so lemme know...
For now, im goin for Age of Apocalypse, despite the Phoenix saga bein the classic that it is. AOA went across a season, spannin 40 books in its entirety, but even just readin the bookends (X-Men Alpha & Omega) is worth the trip. The storyline took balls, and Marvel pulled few punches on it - i still wish one book from this timeline was around, perhaps a plot-based one like Sin City, but then it prolly works better 'casue it ended on a rather high note.