It allowed the Germans to focus on a one-front war. It enabled things like the Blitz, and the 30 days of bombings of London, of the overrun of France and the Netherlands. Whether the Soviets sent troops planes or armor is irrelevant. The Molotov-Ribbentrop Pact was a betrayal. All so that Stalin could run some mass-extermination and land-grabs of his own.

The Russian people fought valiantly, and should be honored for their countless sacrafices, their bravado and their heroism. But they were fighting their way out of a hell that their own leader put them in. I think most folks in the West take that into account and thereby limit their sympathies for Russian sufferings and their reverence for Russian military contributions. It's usually easier to feel better for a guy who gets mugged on his way home from work than it is for the guy who got mugged when he was selling dime-bags out on the corner.