Fan service, or does the X-Men crossover pic actually have something actually to say? Who knows, but the trailer company they hired to cut this should be fired for slapping two of the most over-used trailer background music (from the Sunshine soundtrack and The Thin Red Line soundtrack). Both pieces have been used in far better trailers (The Adjustment Bureau uses the former and both Pearl Harbor and 12 Years A Slave, use the latter).
As for X-Men: Days of Future Past, the cast he is positively loaded with talent, but the issue was always too many cast members, now they have practically doubled things by moving across time lines. Judging from what we are teased with here, the whole thing is consistent with the X-Men franchise (now back to its original director, Bryan Singer) but offers little to get excited from beyond the excessive fanboy factor (and timeline continuity splitting was also recently done with the Star Trek reboot). Time will certainly tell as they cut better trailers for this property.
From Wikipedia (on the comic-book source material which is impossible to tell if they radically rewrote the film or not, so take with a grain of salt):
The storyline alternates between present day of 1980, in which the X-Men fight Mystique’s Brotherhood of Evil Mutants, and a future timeline, taking place in 2013, is caused by the X-Men’s failure to prevent the Brotherhood from assassinating Senator Robert Kelly. In this future universe, Sentinels rule the United States, and mutants live in internment camps. The present-day X-Men are forewarned of the possible future by a future version of their teammate Kitty Pryde, whose mind traveled back in time and possessed her younger self to warn the X-Men. She succeeds in her mission and returns to the future, but despite her success, the future timeline still exists as an alternative timeline rather than as the actual future.