I'm interested to know what you think might be the difference between 'personally significant' and just 'things that I like'.
The Messiaen, Feldman and Ligeti fall into both categories; I return to them often to listen to but they were doing new things, as far as I was concerned, and also encouraged me, as a non-musician and non-composer, to get hold of and study the scores, gaining some insight into what's going on. Whereas the Stockhausen pieces were my first introduction to contemporary piano music when I got an LP from the library many years ago, so they're significant for me but I don't listen to them now, except when there was a discussion here (about no 9 I think). There are pieces which I like but which aren't particularly significant personally eg Tippett's 2nd Sonata, Prokofiev's War Sonatas.
I think Prokofiev's middle sonatas *are* particularly significant, given a) their influence on subsquent Russian piano music (think Slonimsky, Shchedrin etc), and b) their extremely frequent international performances from pianists ranging from students to Richter and Gilels, and c) their central place in Prokofiev's output, and d) their frequent pianistic innovations. I like nos.6-7 only a little, and no.8 quite a bit more, by the way, so personal taste is not really an issue here.
