It's been around for awhile, but it is among the 'classics', as far as I am concerned. X-1999 has to be my all time favorite. The TV episodes, not the movie. A CLAMP project, the main theme is two opposing forces that decide the fate of the world, the Dragons of Heaven, and Dragons of Earth.
That being said, it follows the fate bestowed to the two leaders of these factions: Shiro Kamui and Monou Fuuma, two friends and initially unwilling puppets in the end of the world...until Kamui unwittingly chooses his side and sets Fuuma spinning full tilt into the opposing path.
That is all I will say regarding the series, as it will give plot away.