Dearest Third Cousin,
It's just so good.
Haim are officially my music obsession of September. If you like "Forever" (the song above) check out "The Wire" and then the rest of their EP also called "Forever". Comprised of "three sisters and one mister" Danielle Haim (Vocals, Lead Guitar), Etse Haim (Vocals, Bass), Alana Haim (Vocals, Rhythm Guitar, Percussion, Keyboards) and Dash Hutton (Drums). They fuse a folk sensiblity with R&B beats and have been described as Fleetwood Mac meets En Vogue. Sounds like a disaster right? but their music just creeps into your brain and the next thing you know you've played it 21424141 times on Youtube and have written a blog post about it.
However if the music doesn't do it for you their style is just as good.
Oh and their supporting Florence and the Machine on their Autumn 2012 tour and just finished supporting Mumford and Sons so what other recommendation do you really need?