Without Ukraine in the Union, there will be no Molotov-Ribbentrop pact. In fact, the SU will struggle more than OTL to survive the troubles of famine and crash-industrialization without the rich foodstuffs and peoples of Ukraine. And any attempt to reclaim it violently will immediately lead to western support for Ukraine, defending it against the evil bolshevicks.
Nationalist tensions are still likely to rise in Germany, but whether those will lead to Nazism are debatable. It is certainly posible that a extremist movement involving many of OTL's Nazi's could rise, but an equal possibility without the "Paranoia" of the massive Soviet state is a communist Germany, which would be a natural ally to the Russian state.
Some sort of WWII where a Commie Germany attempts to reverse the limitations and territorial adjustments of Versailes, allied with a Soviet Union trying to reclaim Russian territories in Eastern Europe would be most interesting. This could paradoxically lead to a much less Russo-friendly or Socialist-friendly France. Fascism will also likely be much more attractive to the west with a large Communist state on France's border.