Possibly the dumbest movie I've ever seen, primarily for one reason. Beast. There is an entire line of X-Men comics arguably more impactful than the DOFP storyline involving a cure for mutant powers. Not only does Beast have what is essentially that cure, but it's controllable and apparently also cures paralysis. It's just like his fucking "power boost" formula from First Class; it's a retarded origin story for his blue fur that serves no real purpose, but would actually have a major impact on the X-Men universe. The only reason I can think of for including that stupid serum in DOFP is because Xavier is so powerful that they couldn't think of any problems he wouldn't be able to solve in the blink of an eye.
I also hate when superhero movies try to cram some sort of half-baked theme down your throat (just watch Batman Begins and drink every time they say the word "fear"...). In this movie, the theme seemed to be about how murder isn't a solution, but they put it all on Mystique, saying if she kills even a single person then she's lost forever. I'm sorry, but considering she's been a mutant terrorist for anywhere from 1-10 years (due to an already janky timeline), it's insane to believe she hasn't killed anyone, even accidentally.
They made Magneto into a straight-up moron. You already prevented Mystique from killing Tyrion, you don't need to jeopardize the entire mission to try to kill her now. Oh what's that? You just exposed mutants to the entire population? Oh what's that? You set a Sentinel on "exterminate mutant" mode and were surprised when it targeted you?
They also put in probably a dozen characters that were simply there to fill trailer space and make fanboys jizz themselves in anticipation of the film's release. Blink did some cool stuff, but really Toad, Colossus, Havok, Ink, and every other mutant seen in the previews was in the movie for maybe a total of 10 minutes. I'm a Colossus fan and was lead to believe he would actually be in the movie. I didn't expect to see him be completely useless and die...twice.
Finally, using Mystique's powers as the basis for the adaptive Sentinels makes no fucking sense; that's not how her powers work. In X-Men, when she turned into Wolverine, her claws didn't have the durability of adamantium. She can change her appearance, not adapt to any threat (that would be Darwin from First Class).
I could fill pages with my issues, but I'll go ahead and end my rant now.