I played the Grieg whole sonata for my college juries last year. The 1st mvt itself is not too bad on the hand, but putting it all together is what makes it difficult. I found the middle section VERY hard, (wrong key choice on Grieg I think), and can be hard to make it sound musical. The ending is very fast but some practice should make it decent. Musically, there isn't much, but that's the difficulty, making music out of what he gives you. Nevertheless, I think it is a fine Romantic Sonata. Btw,...ppl say the 3rd movement is the best of all movements!
Brahms Intermezzo Op. 117 is quite difficult in my opinion. Some of the streches and legato playing requires alot of attention, and most importantly, maturity is need to master Brahms. I actually learned Brahms after Grieg, (found getting what I want out of Brahms more difficult but each are quite different pieces)
Finally, Debussy Toccata, Fun fast piece, but quite hard, almost as hard as Ravel's Toccata. A finger-working piece.