Tolstoy has the aesthetic/philosophical insight of a thin-lipped Puritan. His conclusions are dogmatic and authoritarian. What is art, according to Tolstoy? That which gives communal emotional expression in glory of God. All else is vanity, alas: mere self-indulgent Hedonism. Follow the precepts in this book and watch your horizons begin to narrow. The fact that Tolstoy was a distinguished novelist and that he spent so much time thinking about these matters is of no consequence. As many have said before, Tolstoy was a very good novelist but a very bad philosopher.
Tolstoy was a great writer, and his late period of "saintly" simplicity and "solidarity" with the Russian peasants (whom he continued to use on his land) is important to understand as an example of something--I'm not sure what. Maybe as an example of the contradictions of that kind of utopianism (see Isaiah Berlin's great essays on Tolstoy). Also, What is Art?, which dates from this last period, makes some important reminders about the social context of art. BUT ...
It is also the classic example of Philistinism, casually dismissing great works of art because they don't conform to St. Leo's late ideal of simple, straightforward form and content. The previous reviewers make clear the dangers of this kind of attitude--when they don't understand a painting or poem, it couldn't possibly be because there's something lacking in their response. It must be because the work is decadent or wrong. Such an attitude ultimately leads not to the simple purity Tolstoy envisioned, but to the sort of dumbing down we have in American television, cinema, and "beach" novels. "I know what I like" has become the manifesto of boorishness, adding self-righteousness to poor taste.
Tolstoy's What is Art? is worth reading, but keep in mind that his descriptions of music by Wagner or Beethoven, various novels, etc., are ridiculous caricatures that have little to do with the real thing. Furthermore, it's difficult not to see "St. Leo" as incredibly hypocritical, staying in all summer reading the latest novels while his peasants work in his fields, and then criticising the novels because they're remote from the common life of the peasants.
If...you've ever been baffled by a Monet exhibit or a Beethoven sonata, it doesn't mean that these are no good and you may as well go back to your sitcoms and soaps. It means you need to look and listen again, and maybe think a bit. The rewards are there if you're willing to get off your intellectual butt.