They Were Both Pretty Terrible
I own two Spider-Man and two X-Man movies, the first two. Not perfect films but I enjoyed them immensely. I have also seen the third installment of both series as well yet I do not own them. That's because I was not a big fan of either of them. I know I know, but I just fucking hated them.
See with X-Men the Last Stand, well, the way they were just killing characters and misusing others, it was just crappy. They couldn't have done a better job than that? I know the director left to go work on Superman Returns and even Cyclops was in Superman Returns, but still, why did it have to suck so much. It had some cool moments sure, but still, that movie can fucking blow me. They could have just done the Phoenix Saga and there wouldn't even be any need to add any space aliens. You could just say that she is an Omega Level Mutant. They have those now so I'm sure that would be fine. Maybe they did I dunno, but they should have just done a Phoenix story. No cure, nah uh, leave that shit out. And what was up with Psylocke? Sigh. Come on. If the others can't make it because of scheduling conflicts just have the people that can be on a team and go out on a mission. They can get cut off somehow, plane crashes, whatever. Maybe the people who can be in the movie are off on a training excerise with some students and they get attacked by something, maybe Phoenix. Phoenix begins going on a rampage and destroying everything in her path. The government okays the deployment of Sentinels to hunt mutants. The school is surrounded by Sentinels so the rest are still cut off. Only the team that's out there can stop Phoenix and try to do something about the Sentinels before its too late. I don't know, that needs to be worked on quite a bit, but I really hated X3.
Spider-Man 3, gahhhhhh! Well, other than his "dance" there was other stuff I hated. Really they should have had and killed Gwen Stacy in the first movie but since they didn't I say leave her out of this series. Then there's venom. Sure go ahead and bring in the symbiote in one movie, introduce Eddie Brock, but don't try to cram Brock becoming Venom into the movie. The following movie should be all about that conflict. I'm still for Man-Wolf being in that movie. J. Jonah's son was in the previous movie afterall. Instead of him getting a moon rock they could have come up with some other reason I bet for him becoming Man-Wolf. Maybe on reentry from a mission in space his ship crashes because it was hit by a meteorite which is the symbiote. Spider-Man arrives to help get the crew out and the symbiote attaches to him then. Well, J. Jonah's son is badly injured. J. Jonah believes that it is because of Spider-Man. This doctor offers an experimental cure that might save his son's life. It heals him but makes him beastial. He never has to transform and get all hairy, the serum just brings out his instincts. They could say that the regenerative properties came from a Canadian experiment (ohhh tying in some Weapon X, is that Wolverine or Sabertooth's DNA making him act so weird?). And J. Jonah's son probably hates Peter because he straight up stole Mary Jane. Harry still hates Pete and Spidey so he could be helping Man-Wolf out. And forget Man-Wolf's pants or whatever he doesn't need to "wolf out". He can just have super strength, agility, regeneration, reflexes, that kind of thing and he'd still be a threat to Spidey. J. Jonah could be all disappointed in his son's monstrous turn, he could ask Spidey not to hurt him something like that or he could just blame Spidey for all this. The doctor who administered the cure could be some other villain or some guy who was working for Norman Osbourne, whatever. End fight has Spidey almost killing Man-Wolf because of the symbiote but he tears it off like in the movie at a church and it falls onto Eddie Brock. A little wrap up afterwards and the movie ends with a shot of Venom climbing down Peter Parker's apartment building. There's some other elements that need to be in the movie too. Like what is going on with Harry, Mary Jane, Aunt May, and Dr. Conners too.
But I just think they really messed up with those two movies.