For me, Nancarrow's work functions best when he illustrates the sheer possibility of the keyboard freed from the limitations of a human player or players. The player piano in Nancarrow's work is an acrobat, ready to twirl on wires from which human piano players are unable to dangle. I find least satisfying the experimental works which are centered less on the possibility of the player piano, and more on the synthesis of 30s jazz into a unique classical aesthetic. I freely confess to being a listener rather than a musician in my own right, and some of the experiments just don't keep me hooked.
Still, if you're longing for something quite different and of high quality, Nancarrow may be what you are seeking.
You may not be quite lucid after hearing something like Study No. 25, which has 1,028 notes in its final 12 seconds, or one of my favorites, the so-called "Canon X" (No. 21). It begins with two musical lines at opposite ends of the keyboard: the bass starts slowly and gradually accelerates, the treble begins in a super-fast blur of notes at the highest end and gradually descends, becoming ever-slower. In the middle of the piece, these two lines cross each other before they continue on their separate ways.
In study after study, Nancarrow explores complex relationships between meter and pitch, most of the time with absolutely astounding results. Some of these pieces are a bit more relaxed, with blues and jazz elements giving them an almost homespun quality. But soon the blizzard of notes returns, as the composer makes full use of the player piano's capabilities. You almost can't believe what you are hearing.
A word of caution: You probably don't want to program all five discs straight through. Well recorded as it is, the timbre of the instrument becomes wearing on the ear after awhile. Give your ears a break and to listen to something completely different, like Debussy, Copland -- or maybe Bob Dylan.
An essential collection for some -- I'm not sure whom! -- but something every listener should hear at least once.