Although it's sad to see the arts coverage go, I suspect that the decline of the Sun has to do primarily with other more pressing issues, including the fact that its original and chief financial backer, Conrad (Lord) Black, is now in Federal prison for corporate fraud.
About a year ago I tried to read it daily for a couple of weeks. I found the news coverage -- for instance, the kind of story selected and the amount of space given to each -- to be spotty, unbalanced and very much influenced by the editors' (and their former patron's) political biases.
Those wishing to learn more about these matters should check the Wikipedia entry cited by Andrew73.
http://en.wikipedia.org/wiki/The_New_York_Sun