Well, there seems little else to talk about, so I might as well add to this previously deemed worthless thread.
I don't understand how this could not be the last X-Men movie. I continue to hear that there are many possibilities with which this franchise can be taken, but I don't see it so long as certain players are not present. Also, many main storylines are entirely too convoluted and require too much explanation or prior knowledge . . . I think the general audience reaction would be, "What the hell? . . ."
Mutant Massacre - To me, this is most likely the best candidate of any storyline, but is hardly enough to sustain a franchise for multiple movies . . . and just having it as a fourth would detract from the powerful message of the other three.
Fall of the Mutants - Certain aspects may work, others definitely don't (i.e. inter-dimensional portals, Roma, etc.)
Inferno - Can't be done without Cyclops or Jean
X-Tinction Agenda - This is an interesting run, but is a bit over the top for general audiences (Cameron Hodge = giant immortal robot . . . I rest my case).
The X-Cutioner's Song - Good luck with this one . . . Apocalypse, Cable, Stryfe, the Legacy Virus, alternate timelines, etc.
Fatal Attractions - Too much to include and explain--Acolytes, Asteroid M (not believable), Magneto (who should probably no longer be the villain of focus), etc.
The Phalanx Covenant - I have no earthly idea how this could legitimately be done . . . and without almost ripping off Terminator to an extent.
Onslaught (not that it should be done) - Can't be done if Xavier's dead.
While some storylines, such as the Dark Phoenix Saga, have hokey elements in them as well, after their removal there still remains a relevant, powerful story. I don't think the same can quite be said for the likes of the majority of these storylines.
Actually, I almost agree with the poster of this thread. I think the X-Men should take some time off and then come back (not necessarily an entire reboot) with all main characters intact with new actors . . . otherwise the franchise just gets drawn out and long in the tooth.
If they could get all the main characters and original actors back for an X-4 . . . then maybe something might be possible, but I don't know what.