My understanding is that they used to be a bunch of friends who got together every summer and made an album, and that every album was completely different. Once they all finished education, they'd accidentally made it big, so they became full time rock stars.
I listened to their "breakthrough" album (Merriweather Post Pavilion) and it didn't do anything for me, so I haven't bothered exploring their back catalogue, but I understand it is fairly diverse.