HiI just want to say that the less known Variations on a theme by Schumann Op.9 are really Wonderful!!!They are really romantic, in Schumann style , some (4th, 11th) are really poetic. (I am desperatly looking for a free sheet in Internet).Possibly they are technically less brilliant than Handel Variations (for many people the most amazing set of variations since Bach's Goldberg). But as a music work they are one of the most melancholic and romantic pieces I've heard. (they were dedicated to Clara when Schumann was mentally ill, with strong depression).
I just played these variations in concert about 2 weeks ago. They are incredible, but they are also MUCH MUCH harder than they look. Brahms gives you some ossias, but they are really much inferior to the original measures. They are also incredibly difficult in terms of sound-form and subtle things (phrasing, colours, dinamic levels and such). They are of moderate difficulty if all you rate is how fast you can move your fingers though (and even then, there are some passages that are quite difficult).Id be glad to help with any specific questions you may have about this great work.