Late Beethoven works are astonishing. The Great Fugue [1,2] is also remarkable -- fiendishly tough on both audiences and players. It is hard to believe it was written during the early 19th century. The fugue also has an interesting story: originally the 4th movement of a quartet, its terrible reception caused the publisher to request a new 4th movement, and the fugue became a standalone piece. The best description I've heard of it is from Stravinsky: "a contemporary piece of music that will be contemporary forever".
At the end of the YT video, the audience applause seems tepid, nobody stands, and yet the performers must be exhausted. (I think it's a great performance.) There's no singable theme, nothing really catchy, just 15 minutes of pretty intense focus required by everybody. For me, it's completely gripping - it can't be background music and I cannot do other work if it is playing. I think it is somehow alien, and so it will never be as widely celebrated as his other works.
[1] https://en.wikipedia.org/wiki/Grosse_Fuge
[2] https://www.youtube.com/watch?v=13ygvpIg-S0