I've loved Robert Simpson's music ever since I first heard the 9th quartet about 12 years ago and have collected most of the Hyperion series of recordings. That quartet is still one of my favourites.
He has a very distinctive style throughout much of his output, so I wouldn't want to sit and listen to a whole concert of his music (but that applies to most composers I can think of). I'm fortunate that I've been able to programme a couple of his chamber works in the concert series that I'm involved in planning.