I would guess that Rachmaninoff was a pretty melancholy guy. I haven't read much (really anything) about his personality, specifically, how he presented himself and interacted with others. If I had to guess, I would think he was very professional, always trying to be cordial. I bet people saw a great depth of character in his soul by looking in his eyes; and his sincerity in music probably mirrored his genuineness in life.
I think of Prelude #6, Op. 23, written the day his first daughter Irina was born. On the surface this piece is mystical, flowing and beautiful, but underneath there is a sadness. When I listen to this piece, I can feel the genuine hope and humbling sense of responsibility he probably felt that day.
Rachmaninoff's music makes me aware of the complexities in life and how beauty and happiness are often hidden by the distractions of everyday life. Just think of the cadenza in the first movement of Concerto #3, the alternate version (ossia). There are numerous voices there that sound like they are communicating with each other, each having their own opinion but not really arguing, almost socratic. And in their interaction, the actual conversation, there is beauty.
I can't play this piece, but I wonder what people who do, think of the idea that the voices are speaking to each other? And do you play the ossia or the more scherzo-esque "regular" version?
Rob