Italian artists are also well represented (notable were amazingly sizable collections of Titian and Caravaggio) but the gems of the collection are obviously its German, Flemish, Netherlandish, etc. (aka: 'Northern European') holdings, because they're simply so massive. An artist like Dürer or Peter Brueghel the Elder may be represented with 1 or 2 paintings in an American museum... they're very hard to find these days and he's not making any more of them; so to see SO MANY Dürer masterpieces, in oil, in one room (and this happened room after room with an entire roster of A-List artists) was a bit overwhelming. But it was overwhelming in a 'good' way, if such a thing is possible!
The story of the collection is basically the story of the Hapsburg dynasty. A family that ruled Europe for 6 centuries by marrying into the royal families of every other country in the region. The artwork at the Kunsthistorisches museum is almost entirely the art of the Hapsburg dynasty.
It seems the main reason the collection is still so strong is that Vienna was able to defeat Napoleon (who was, prior to this defeat, believed to be unbeatable) when he came around looking to further-fatten up his trophy house: The Louvre. All the museums in Vienna have mind-blowing collections because all of them escaped French plunder.
Anyway. This family knew a thing or two about collecting art... check out the paintings (we only visited the paintings... but maybe we'll go back for more). My camera *really* needs to be replaced... sorry about the poor picture quality.