One of the coolest special effects in X-Men: Days of Future Past was the Quicksilver "frozen time" effect where the character is moving so quickly that everything around him seems to move in super slow-motion. In this video, director Bryan Singer explains how they achieved the effect.
If you're too impatient to wait for opening day on May 23, here you have a sneak preview of the opening battle in X-Men: Days of Future Past, now clearly showing the awesome morphing Sentinels from the future. The scene shows the mutant hunters invading their hideout.
I read Days of Future Past—the X-Men two-book-saga by writer Chris Claremont, penciler John Byrne and inker Terry Austin—back when it first came out in the 1980s. Based on the new trailer, it seems that is has some key moments from it. Like when Storm gets killed?