During my music education I was more focused on classical styles of western composers up until times of Beethoven. Namely, I understand the structure and some ideas behind music by Vivaldi, Bach, Haydn and how to find similar pieces if I want to.
The symphonies of late 19th century, not to mention what comes later, already sound exotic to me. With time I came to appreciate Rachmaninoff, and his approach to harmony is among my favorite one nowadays. I understand that it relates to the late romanticism, and if I want to look for something similar, I can try e.g. Debussy. I don't particularly like avant garde music, of which I had to listen a lot to Prokofiev and Stravinsky, but at least I do understand some reasons behind their approach and again, I can find something similar quite easily.
I'm completely lost though when it comes to Symphonies 5 and 10 by Shostakovich. That's more melodic that avant garde, but definitely less harmonic than late romanticism. Which kind of style is that, what has led to it, and how can I understand it best?