I think the Grieg is very difficult! It is really tricky in some places, like the last movement, and some bits in the 1st movement. The opening is very hard to play in public...I warn people now who thought like I did. I had played th opening for years, and never thought anything of it....until I was on the stage....then it went wrong! It's not really that hard, but it is the sort of thing people can bash out at home, and screw up on the stage.
I think it is quite easy to learn, I learnt the notes pretty quickly, and had fun doing so...however playing t a performance level is quite tricky.
Gilels said "It has to many white notes". I think that is true, and that makes it difficult