5. If you are going to add characters that have no business in the movie..at least have AWESOME ones!
With Singer’s track record on the “X-Men” franchise, he likes to add characters to “enhance the story”. If you are going to do that, do it with DECENT characters. Now the rumor is that the cast from the first 3 films is mishmashed with the cast from “X-Men: First Class”, which is an interesting concept, and can fit with the comic storyline (more so than any of the other films). If you are going to deal with time travel and alternate timelines and such, you have some really good characters you can “enhance the story” with. Two such examples of this would be Bishop and Cable, who were in the Days of Future Past story in “X-Men: The Animated Series”. You also have Forge, Rachel Summers and others that can fit into the story if you need to add more characters. So if you don’t stick with the source material, at least you service the fans and they won’t try to burn Singer at the stake.