Most crucial to me is logic. I need to understand why one note follows the next. I also appreciate pianistic fluency in the writing, so that the piece lies well in the hands.
I play through a new work a number of times before I decide whether or not I am the right pianist to perform the piece. I look for innovation, beauty, drama, lyricism.
I seek pieces for which I can be a convincing messenger. Any length, any style. I just need to be touched by the composing, musically.