Djurgården itself is a beautiful area with plenty of room for picnics, wandering or children's play. On weekend afternoons there are a number of residents of Stockholm enjoying the area. For such a flat city it is quite hilly - though not quite what you might expect if you live in a really hilly area. It is very pleasant to get the ferry from the old town, walk to the museum and get the bus back.
As for the museum itself, it is first worth saying that it is worth seeing for the site even if you have no interest in paintings. It was the home of Prince Eugen [1865 - 1947] who was interested in gardens as well as painting and it is really beautiful with a fine view back over the old town.
Prince Eugen was an art collector as well as a painter of some repute himself. His house and his outstanding collection of turn of [19th] century Swedish art were left to the state in his will. Some of his own best landscapes, [his specialism] are on show. Some of the private apartments are included in the price and are little changed.
The garden contains some fine sculpture, work by Rodin and Milles [see Millesgården page] being included.