One of the worst things about the Marvel comic book movies, is the fact that there are a number of characters whose rights are held by different studios, which means that we are not going to be able to see them all appearing in the Marvel Cinematic Universe. There was once a time when it looked like Sony were going to continue ruining Spider-Man for us fans but fortunately they saw sense and agreed to allow the character to join the MCU.
Since then, there has been a lot of talk about the possibility of the Fantastic Four and the X-Men returning to Marvel Studios and joining the Marvel Cinematic Universe. With the last Fantastic Four movie being one of the worst comic book movies ever, you could understand 20th Century Fox allowing Marvel to use the characters in a similar way to Sony and Spider-Man. However, the X-Men movies have been hugely successful and there are plans for plenty more X-Men projects, which makes it unlikely that Marvel will get to use them any time soon.
With that said though, Marvel legend Stan Lee has been talking about the movie rights, admitting that he believes they will all return to Marvel Studios at some point, "Sooner or later, they're going to get the rights back to all our characters. They're working on it, and they're still making 'X-Men' movies and stuff. Don't worry about it. You'll get more Marvel superheroes than you'll have time to look at in the next few years."
We hope Stan Lee is right and we hope it is not too much longer before we get to see all of the Marvel comic book characters appearing in the Marvel Cinematic Universe.