The Piano Trio in A minor is a wonderful piece. But a few years ago, I had a chat with a cellist who appears regularly at our summer chamber music festival in Seattle. We were comparing it to the Shostakovich Piano Trio in E minor. He said, "After hearing the Shostakovitch, you want to go home and slit your wrists. After the Tchaikovsky, you want to go home, pour a stiff drink and forget about it." He had a point. Shostakovich cuts closer to the bone.
The String Quartet in E-flat minor was an ordeal to listen to. Morose or not, it doesn't compare to the first quartet in D Major, which is a classically composed gem. A composer with Brahms' critical sense would have suppressed that piece.
I’ve heard the Tchaikovsky sextet many times and the melodic freshness overcomes whatever structural problems it may have.
You have to be in the mood for the the Third Quartet but if the mood is right it can be quite moving. The trio is like that in that it can seem interminable if not performed properly.
Why is Brahms always regarded as a better composer than T? Both could do things the other couldn’t do.
Tchaikovsky was just about the only Russian composer of the 19th century who could write a convincing Sonata-Allegro movement.