I just rewatched FIRST CLASS and I found the sequence in which the missiles finally explode/fall in the ocean a bit too brief. It was an amazing scene nonetheless, but I expect it to be longer.
What's the biggest action scene in the last third of FC, in your view? I would say that the climax is supposed to be Erik pulling the submarine out of the water, the Blackbird crashing into the submarine and finally Erik stopping the missiles in the middle of the air.
So basically, the sequence of the missiles exploding wasn't supposed to be the action climax of the movie...? I guess so.
By the way, such a compelling movie. Terrific cinematography, and I like the genesis of the X-Men.