I thought that was just brilliant. The whole Van Gogh bit was just enthralling. The Doctor and Amy were great. What a sad story. I almost feel as if meeting the Doctor and Amy and the future that they showed him somehow contributed to his depression even further. Imagine how Vincent would have felt in the days and weeks and months after his incredible chance encounter with the Doctor and his beautiful assistant. He fought aliens and travelled in a Time Machine (which was impossibly bigger on the inside) and saw his work finally appreciated only to have to go back to being ridiculed, despised and lonely once again. Maybe his meeting with the Doctor had such a profound affect on him and after that he just couldn't bare to live such a mundane, unappreciated and lonely existence and he just wanted to be free.
This was my take on it when I was watching the scene in the museum - imagine going back to his life after that! That's what I loved most about that scene, actually - it was at once wonderfully fulfilling - he will
be remembered, and as a genius - and horribly depressing - he will never know anything of it, never feel gratitude or acceptance. A very conflicted thing for someone to go through, I think.