Oleg Rastrenin - I can not recommend him highly enough in everything related to Il-2, Ilyushin in general and "shturmovik" aircraft of VVS in the 1930s-1940s. Ironically, he started his research of Il-2 as a true believer in the Soviet myths of "flying tank", "black death", etc. He changed his mind.It looks very logical: the Il-2 was hard to shoot down, so it took over 36,000 of them to produce. And 9 (nine!!!) sorties per one loss in 1941 also certainly testifies to the IL-2's invincibility.
I really wish that Oleg Rastrenin would finally publish his books in English, so that those who do not speak Russian would finally familiarize themselves with the history of IL-2 based on documents, not Soviet propaganda. The history of IL-2 was very complex and ambiguous. And now, when we know the alternatives (and there were more than one) there is no certainty that the decision to produce the IL-2 on a mass scale was optimal.
Undoubtedly, the airplane contributed to the victory over Germany, but it is a definite exaggeration to consider it decisive. Artillery and infantry were of the greatest importance in the Soviet army, while air force was probably the weakest branch, unless you consider the navy, which did not prove itself at all.
Full disclosure: I belong to the "Il-2 sceptics" club.