I you haven't seen X-Men: Days of Future Past yet, then you might want to steer clear of this video by Mr. Sunday Movies because it's packed full of SPOILERS.
If you saw the movie, I'm sure you were able to pick up on a few easter eggs in reference to the Marvel and X-Men universes. This video completely focuses on those things and claims to point out all of them. It also explains a few of the things that were changed in the process of adapting the comic book for the big screen.
X-Men: Days of Future Past was a spectacular film, and I'm looking forward to seeing what exactly they have in store for X-Men: Apocalypse. Thanks to CBM for the tip.