As we all know, "Let Forever Be" is a down-right GREAT track from The Chemical Brothers: so I won't say much about it... It's really brilliant. "Diamond Sky", the second track, is essentially a remix of an album track: "Surrender", from the album of the same name. Its short and very percussive intro, sets the melody up to a tee. It's a superb remix of a superb track, and as a track on its own, its inevitably inspiring, and will show you that there are things worth holding onto in this funny old world.
"Studio K", the third and final track on the single, is basically the drum track to the FANTASTIC "The Sunshine Underground" from the 'Surrender' album. Good listen, but you may lose sight of its point after a couple of listens. Also, it's very tweaky compared to the original, but still good. (You could use it for a remix for another track)
All in All, the single is worth a buy for dedicated chemical fans, but maybe not for others who don't appreciate them as much as the rest of us.