I have an impression after having read only few works of each. If I put my mind to it and invested some effort, I think I could make a good thesis of it.
Dostoyevski is much more black and white. The good characters are nearly saint-like (Prince Myshkin, the younger Karamazov brother ); the villains epitomize evil (Karamazov's old man, The Grand Inquisitor). Those in-between characters are foolish and perpetuate evil, mostly because they are stupid and fail to respond to evil in themselves or in others.
Tolstoy's characters are more balanced. He's much more sympathetic to his characters, even the bad guys and the foolish ones. I noticed this first with Anna Karenina when I was mentally berating Anna's husband for being such an ass, and then thought suddenly, "You know ... I'm just not sure. Had I been in his situation, I might have behaved the same way."
Of course lots of books have characters that make you question your values, but a great many of those stories are contrived. People who really ARE wise are made to look stupid. People who are evil are made to appear good. Aristophanes can make Socrates look stupid when he's telling his own story. Doyle can make Holmes appear logical, when he's not. But Tolstoy's characters, particularly his central characters, are just like real people - partly because some of them are, and partly because even the fictional characters ACT like real people.
There's a lot of writers whose contributions I think are grossly overrated by intellectuals, or by other writers, or by people in general: Fitzgerald, Ibsen, Melville, Joyce. All of them clearly have or had some keen ability, to be sure, but not so great as they are reputed to be (at least not in my admittedly uneducated and unrefined estimation). I can see how someone would say that Melville is a Great Writer, but I just can't agree that he is, or ever was, the greatest writer in the English language or that Moby Dick was ever the greatest book.
I'm not saying that Tolstoy, as I've occasionally heard, is the greatest writer. But, imo, he's up there. I'm not surprised that others think he's there. I can say that he is among the greatest writers I've ever read and when I hear others say the same thing, I never suspect a hint of hyperbole.
OTOH, Madame Bovary is a solid refutation to the notion that sympathetic treament of all characters is necessary for a Great Writer. This really is a brilliant book, even if the characters are stilted. The druggist (was his name Homais?) is one of the truly despicable characters from literature. Nevertheless, I do wonder - could there really be someone quite that evil?
