The third and fourth quartets, written in 1927/8. The third was written for a chamber music competition, and it won the first prize. There are lots of advanced playing techniques in these pieces, which in itself makes them interesting. For the listener. I don’t know if the players think the same, as it takes quite a lot of skill to get through unscathed.
Bartók is well known for his interest in ethnomusicology. He was comparing different musical systems, and used his findings in his pieces. He was also highly analytical and fascinated with mathematics. This shows in the structure of the fourth quartet: consisting of five parts, the third acts like the centre, with the first and last part and the second and fourth part paired to each other. Like little arches.
It took me a while to like these pieces, but now that I do, I listen to them a lot. Usually in a different recording though.