Complex sentence: It took a long time after Schubert's death before his piano music was taken seriously: until the early 20th century his vast piano solo production was often criticised for being merely salon music, good for inexperienced girls, but not to be taken too seriously.
Split into simpler sentences: It took a long time after Schubert's death before his piano music was taken seriously. Until the early 20th century his vast piano solo production was often criticised for being merely salon music; good for inexperienced girls, but not to be taken too seriously.