Similarly had a really good guided experience at the Vatican. Impressive collection of art, and interesting history, besides.
I "get" Van Gogh, I think. I tend to trend darker in what speaks to me. I found Guernica powerful. Part of that is understanding what Picasso was reflecting on--the history matters to me. Most Picasso doesn't interest me. A lot of impressionism is "pretty," but not very interesting.
Good marble statues impress me. The craftsmanship of making stone look supple is impressive.
Some "modern" art is really cool; a lot of it is completely meaningless. What makes one vs. the other is probably impossible to describe.