I do agree that it was fun to see them working as a team and I do agree that the most frustrating thing about X2 was that we didn't get to see the team together at the end.
However, I think the problem is that the X-men movies were very much Wolverine and the X-men. The X-characters had to be established and the general obsession with Wolvie is unavoidably going to bump the others off the screen.
I'm really keen to see them finish the story off properly with 2 more movies detailing the Fall of the Mutants and the Four Horsemen of the Apocalypse, leading into a Cable spin-off and possibly an Age of Apolalypse spin-off.
I enjoyed First Class but it feels like a soft re-boot. There is a lot more gold to mine in the original franchise's chronology.