How did the Soviet Air Force develop over the course of World War II? How did it compare to that of the other participants?

I was just reading this thread http://www.reddit.com/r/AskReddit/comments/2leqe9/what_are_some_government_secrets_that_have_been/ and there was a bit of talk about the American military compared to the Soviets, and I realized that beyond being outclassed during Operation Barbarossa I haven't really read much about the Soviet Air Force's capabilities during the war.