With the latest Spider-Man installment, the plot was roughly the same as what you'd see in a 90s Batman movie (although it didn't suffer from the other problems of that particular series). With the newest X-Men film, you get something that you haven't quite seen before. It didn't have a completely different vibe from its predecessors the way Captain America: The Winter Soldier did, but it didn't feel like just another installment that will blend in my memory with the rest of them.
As a fan of comic books, I don't think that it's a coincidence that the more the movies take from the comics as their inspiration, the better they tend to be, and this was no exception. Longtime comics readers know that this was an adaptation of a favorite story from the comic books. (I have fond memories of it myself, as a friend of mine gave me the second part as a back issue for my birthday.)
Of course, if you're expecting a direct adaptation of the comic story, you won't get it, but that's not what I'm talking about. What works in a monthly comic book won't work in a movie, especially one that's already rooted in its own continuity (and manages to have as many problems with said continuity as a comic book series that's been running for fifty years). The point is that if Hollywood is going to look to comic books as inspiration, then they should actually look to the comics - not just the characters but the stories.
Anyway, all that said, while I think that it's too early for me to declare that this is the best movie in the franchise (especially considering how partial I am to The Wolverine) it's safe to say that it's one of the better ones. For me, it had everything that I liked about the first two X-Men movies - strong characters, a good story, etc. Lots of people seem to hate the third X-Men movie, but I think that it got a couple of things right - 1) better action scenes and 2) a sense of fun. This movie manages to mix in all of those good qualities. I mean, is it just me, or do the fights in the first two movies look more like funky dances than fights? The fights in this one were much more visceral and compelling.
While the fate of the future is at stake, and that's treated with the appropriate heavy hand, the movie definitely has its fun moments. Quicksilver's big scene comes to mind quickly, but Wolverine's journey back to the 1970s has some comedic value as well, without being ridiculous and over-the-top.
I've heard at least one person say that this is up there with The Avengers. I'm not so sure, but maybe that's because my expectations were raised a bit too high. I will say that it's a good one, and I'll point out that my wife enjoyed it, even though she hasn't been a fan of the previous installments (didn't even bother with The Last Stand or First Class - although she did like The Wolverine). It seems to be a success at the box office as well, so hopefully this means that Hollywood will continue to look at the comics for story ideas. I could make a suggestion or two if they need one.