I don't know about the rest of you, but I haven't seen an X-Men movie yet.
Yeah, yeah, yeah, I saw those films called X-Men that Fox produced, but unlike Iron Man, Captain America, Thor, Dr. Strange, The Avengers etc., they never felt like the X-Men from the comic books to me.
I have no reason to believe that Marvel has hit any sort of high-water mark. They're just starting to hit their stride.
With special effects technology getting to the point that fully digital sets and actors can be done relatively cheaply, I believe we're just at the beginning of seeing films that are truly only limited by the imagination of the creator (which is the thing that made comic books work so well in the Golden and Silver ages when film special effects were highly limited).
There's nothing magical about the Avengers, and I frankly think most Marvel movies we've seen so far have been limited by cost and technology (in hindsight, the original Iron Man, Thor and Captain America films seem very simple with mostly practical effects and clear efforts to prevent the budgets from ballooning when viewed in the context of films we've seen since then).
I still have the irrational fear that Marvel will forget everything they've learned when they do the FF, but that's an irrational fear. My more rational side tells me the best is yet to come.
You ain't seen nothing yet.