I want to say I'm not very familiar with the comics, so I am probably not getting some points. But as a viewer, I don't think this will necessarily be the last movie. I think they are intentionally leaving some doors opened for a sequel, in case they can do it.
And I don't think there were so many "stupid" deaths, as Frozen said. In fact
the only very stupid death is Scott's. He really died in a meaningless way, but it must be because the actor is involved in other projects now, as Superman's one. While Xavier isn't exactly dead. He can come back in a sequel, as the last scene of the movie suggests. In some other form maybe. Not with the same body and all. This will solve the problem with the actor not wanting to appear in X-Men movies anymore. And Jean Grey, too. If Xavier is still alive, maybe she, who was sort of resurrected for this movie as well, will be able to come back. After all, a Phoenix is peculiar for the ability to come back to life after death.
I also think that the mutants who have lost their powers will get them back in a way or another. Maybe The Cure wasn't a final solution, maybe it has only temporary effects, as the scene with Magneto sitting at the chessboard suggets. He seems to be able to use his powers after being injected with the cure, so why the others shouldn't be able to have their abilities again?
I think the movie wasn't that bad overall. They tried to make it shorter than the story actually required. Some characters needed some more space to express themselves. Some others were not developed at all. Some others were completely absent without reasons. I mean... I was expecting to see a Colossus/Juggernaut fight, I was expecting to see Nightcrawler, I was expecting more parts with Angel and more development in Rogue's character, etc.. etc... Maybe if the movie was a bit longer. The script was clearly cut in some points to make it shorter. I don't know if this movie was condensing what was originally more than a movie into one.That was tthe impression I got. But it wasn't that bad as many say. Just not as good as it could have been.