you wouldnt be able to do a direct lift from the comics, say if you were to do a direct lift from a story like phoenix saga... you have no explination of where and what the characters doo, only the fact that one of those characters in the group has become the phoenix and the others must fight to help her.
Were as, the animated series toned down tuns of comic stories into 5 series...
There wouldnt be a big cast, just consistant and more development for the characters. If i was to sum up each series of the x-men animated series as one x-men movie.
x1 - would be about senitor kelly and the registration act, Magneto's war, Sabretooths and Wolverines rivially being explored, the extent of some of the more powerful mutants and what there capable of and the enslavement of mutants by humans which fuels the magnetos war. Leading to a pinical moment where you have the idea of sentinals.
x2 - would see futher development of Cyclops and Jean's relationship, Mr Sinisters interest in making the perfect mutant, Storm tackling her own demons from the past, Wolverine on his bid to find out more about his past turfs up some more unsavoury characters. Rogue and Mystiques mother daughter past revealed. leading up to Mr Sinisters master plan and Magneto/Xavier working together. after being villians in the first movie, they fight together in the second. the story would also have some legacy virus feel to it.
x3 - would be more focused on the phoenix saga, to which you explore more origins of each character at the same time wolverine fights his feelings for a woman who has become all powerful and at the same time is already taken by cyclops who has to stop the women he loves. The whole story would span xaviers past right up to jeans past and what happend in the previous two movies.
x4 - would possibly focus alot more on wolverine - maybe even more of a solo movie with wolverine finding about his past in Japan, however there is also an apocaylpse/the twelve kind of story happening so it could be a two seperate stories that joins together.
x5 - would be more of a story closer, with some big event leaving the x-men limited in numbers, maybe xavier dying.