Glenn Miller wrote:

>There are certain composers who died young and showed great promise, yet
>not producing great works in their last few years--does Mendelssohn fit
>this description?

Yes, and yes again: Schubert.  Mozart also had a future, obviously.  But
Schubert is the one.  Grillparzer was the one who composed the epitaph:

   Here lies a great artist, and even fairer hopes.

Had Schubert lived and worked another twenty years I believe the entire
course of music would have been different.

Bill S