After X-Men 3 the franchise was left in a shambles. Attempted restarts didn’t do much, Wolverine: Origins was pretty terrible, The Wolverine was fair. The best thing out of the last few years was X-Men: First Class which respected the original material yet still managed to appeal to mainstream audiences.
Apparently 20th Century Fox realized after watching the core Marvel movies that there was gobs of money to be made in a shared universe so they invested in combining their main X-Men stories with First Class. I was worried about it originally, but it seems like they may have their act together. It helps that they are taking Days of Future Past, which is one of the most important and popular X-Men story arcs ever written as their source material.
20th Century Fox owns the rights to all things Marvel that have to do with Mutants a decision that Disney/Marvel is probably regretting at the moment. I like the competition, but wish there was a way for the two parties and Sony (Which owns the Spiderman license) to hold hands and make nice. It would be mind blowing to see three large studios tackle continuity and share characters.
As far as the trailer goes it is fantastic to see characters that I grew up with in the flesh. I expect that most of them will only appear briefly, but better that than thinning out the story by trying to give everyone equal time. We still have to wait till the end of May to see if Fox succeeded, but for now they have my interest.