I have a limited interest in modern art. But the Museo Reina Sofia is great! At 3 euros, try it!
For a start, the museum is physically pleasant--a nice interior courtyard with benches and people, halls looking down on the trees, some air conditioning, good traffic flow, and amusing clear elevators.
The second floor has Dali paintings: some are interesting, some bizarre, some engrossing. In between, I looked at the Miró paintings, which are mostly cheerful but still really Art. Of course they have a fair number of Picasso's works, including Guernica.
Third floor has, among other things, amusing modern sculptures--mobiles and, oh, other fun stuff.
Excellent photo gallery: works by Man Ray, Strand, Steiglitz, Walker, Steichen, Atget and good examples by them too.
There was also a large exhibit of a Spanish photographer, Catala-Roca (sp?) whom I'd never heard of. Great stuff, and mostly set in Barcelona or Madrid which added to the pleasure.
Most modern art museums are "challenging": full of man's inhumanity to man, or the insignificance of man, or just cramped or noisy. This museum has works, like Guernica, about war and evil and sorrow--they are part of art and life. But I can be thrilled by Toledo including its dark aspects of the past without that edgy "challenge" feeling of some modern art galleries. Museo Reina Sofia is the most enjoyable modern art museum I've visited.