This is pretty much the main reason why I went to Vienna. I've been a fan of Pieter Bruegel since…read morehigh school and this museum has the largest collection of his art in the world. I pretty much spent an hour sitting and looking at their exhibition of his paintings.
While most of the art here is Renaissance or just after (and mainly Dutch, German, Italian, and French), there's other good stuff as well. If you like Spanish paintings, there's a lot of Diego Velasquez. Many of the exhibits have German and English descriptions of the art, but there are some that just have German, especially the ancient Greek/Roman and Egyptian parts of the museum. Of course, there are exhibits on relics from the Austro-Hungarian empire. The second (or kinda third) floor of the museum does not have much in terms of exhibits but has an extensive coin collection from that former empire. I liked some of the model ships they had to entertain the royalty during their long dinner parties.
Knowing that I would go to other museums, I opt-ed for the 7 Museums annual pass for 53 Euros (as of this writing). It's worth it only if you go to at least two other museums. Just going to the Neue Hofburg across the street and the Imperial Treasury further down will equal the price you paid. I went to those, along with going to Kunsthistorisches another time and Imperial Carriage Museum at Schoenbrunn Palace. You also get re-entry privileges in case you wanted to get some food, because the cafe seemed pretty "touristy" here. Note, this pass does not get you into the Sisi Museum (or related ones)
There aren't a ton of restrooms at this museum, so plan accordingly. You could probably cover this museum in about 90 minutes.
