Corno Dolce, Greetings !
Messiaen's 'Regards . . .' - 'fun to play' ?!
I haven't tried; I don't have a score. But the small amount of Messiaen I have played, some of his organ music, I find difficult (even 'Le Banquet Celeste', which must be one of his easiest pieces). However, Messiaen is a great favourite of mine and for me his music is rewarding, inspiring, breathtaking and overwhelming, but not 'fun'.