Have you previously played Messiaen's music?With regards to accessibility, I think there is a difference here between accessibility to the performer vs accessibility to the listener, especially an audience not accustomed to this kind of music. Some of the more accessible-to-the-listener pieces in the set (at least from my observations), are not necessarily easier in terms of difficulty to the performer. In the big picture selections from Vingt Regards are probably easier for a recital crowd to digest than something like Catalogue d'oiseaux. I would recommend obtaining the score and playing through the sections that interest you. Some of the difficulties in playing this music are not directly apparent when just listening to a recording.