I have played exactly two games of Diplomacy, both on the same day. There won't be a third game, ever. It is long, repetitive and boring, with a strong possibility of an endless stalemate. The highlight of the two games that I played was that somebody brought a box of Dunkin Donuts, and I ate two of them.
However, I do enjoy playing A Game of Thrones, even though the mechanics are clearly inspired in part by Diplomacy. AGoT has more strategy, more depth, superior components, and interesting mechanics.