After Reading this part in the book, I see what all of you were saying about his love for nature.

(quote from the book)- He smelled the garden, the yellow shield of light smote his eyes, and he whispered, 'Life is so beautiful'.

I think the Don was happy were he died: his peaceful garden. I also think that he was glad that he didn't die in a pool of his own blood(which is were most gangsters die), instead, he died in the most peaceful place on Earth.