A group of museums is probably an unusual World Heritage Site, but in this case there can be no doubt that its statuts is deserved, and there are very few other sites in the world that would earn a similar distinction (I'm waiting for the US to nominate the Smithsonian Museums, though). Great monuments to the Age of Enlightenment, all museums (at least the ones currently open, as there is a massive amount of restoration going on) are interesting, but the Pergamon Museum tops them all. I would say not even the British Museum (which is a really great institution) can match the archaeological contents and the interior of this building (well, maybe they are equally good). The Berlin Cathedral next door is also very interesting, especially the view of Berlin from the top. Nobody coming to Berlin should miss this area (and will not, anyway, because it's right in the centre).