1. Nightcrawler is to Quicksilver as Quicksilver is to Nightcrawler.
Both action scenes feature a major infiltration for their own purposes, one that leads to a challenging infiltration with everything going haywire, the other too simple and fun with not a single cop posing any threat, now that's how super speed comes in handy, unless you could teleport your way around the place. Either way, it's a bloody damn good set up for an action sequence and makes me all the more excited for 2016's X-Men Apocalypse as I hear it features them both together!
2. Both have the same director.
Remember how X2 had a plot so advanced it targeted the entire world at once?! Well, that must have been really cool for any movie back in 2003 and one could have told Bryan Singer would surprise us again in another comic book flick, let alone Superman Returns. Also, the score was yet again composed/ edited by John Ottman.
3. Both have the same villains.
X-Men: Days Of Future Past explains a little more about Stryker and Magneto at their earlier stages (though in a slightly modified timeline) with some similarities in comparison to X2, such as some information regarding Stryker's son, Jason, who appeared to be the master plot of X2, or even how Magneto and Mystique got along or separated a while since the final encounter of X-Men: First Class (yet again a matter of two different timelines but the purpose is to merge one with another and neglect what's erased) , or simply how Magneto, from the very beginning fought for the greater good of his fellow mutants, serving as the bad-good guy (in both timelines, makes sense that Wolverine thinks he was always an asshole!)
4. Mystique ends up hooking up with someone to advance the plot.
As usual, Mystique enlightens us on a specialist's infiltration style that is seemingly flawless especially in terms of voice.
5. Both happen in the real world in the sense they involve politics.
X2 had a global impact so vastly terrifying it had to be brought to presidential notice, while X-Men: DOFP focused on two powerful mutants that were accused of being involved in the assassination of president Kennedy, or probably because of the general fact that the world lacked counter-measures to fight mutants.
6. Other possible similarities.
X-Men: Days Of Future Past probably succeeds in the sense that it remakes several things X2 did in bigger and better ways suited to the need, plus sets up a fresh start for 2016's X-Men: Apocalypse, starting with the En Sabah Nur reference from its post credits scene. What other similarities do you think exist between these two sequels?