I don't think it's possible to describe this song, never mind do justice to it, but I'll have a shot.
This is, quite simply, a wonderful song: amazingly euphoric, unashamedly melodic, hauntingly beautiful.
If you like Mercury Rev, you'll love this.
Even if you have never previously 'got' Mercury Rev, you would be hard pressed to dislike their song: it has an immediacy and a accessibility which I think much of their other stuff lacks.
And if you've never heard Mercury Rev's music before, I can't think of a better place to start.