(bits of spoilers back here)
I loved how this wasn't an episode about depression--it had that in it, and handled it well, but the story was about beauty and art and hope.
The Doctor: The way I see it, every life is a pile of good things and bad things. The good things don't always soften the bad things, but vice-versa, the bad things don't necessarily spoil the good things and make them unimportant.
(the part I liked best, there, was the addition that bad things don't make the good ones unimportant. YES.)
Cazaril's prophecy to Royina Ista never fail to make me cry. And they could have been said to Vincent, too (in fact, one could say that the scene in the art gallery was a visual and verbal equivalent to this speech), or to anyone like him or Ista, whose life has been entirely overshadowed by a curse.
When the souls rise up in glory, yours shall not be shunned nor sundered, but shall be the prize of the gods' gardens. Even your darkness shall be treasured then, and all your pain made holy.