For me, it's the slow movement that stands out. How does she achieve that eerie telepathic union with the woodwind players? And of course the endlessly elaborated hemiola is hypnotic.
Also, worth nothing: Rachmaninov wrote a huge amount of vocal music (more than just about any of his contemporaries) and lots of large, ambitious sets of variations (ditto.) I have always felt that the composition of variations is where you see the true measure of a composer.