If you could remove Comrade Stalin from picture then Communist Miracle could run for quite some time.
IOTL even with Comrade Stalin communist system did provide ever-increasing quality of life for an average Soviet citizen up to late-1970s, with exception of 1929-1933 (forced industrialization and Holodomor caused by it) and 1941-1947 (WWII and immediate aftermath), not as effectively as 1st world, but more effectively than 3rd world or European colonial possessions. It is hard to predict how would leadership game among Commies play out, and we're trying to discuss economy here anyway.
Poland would eventually fall communist due to being shoehorned between the two.
The threat would be there, but I'm unsure of how events would play out. Remember, IOTL Baltic countrilets existed for more than a year in a world gone FUBAR (a.k.a. WWII) before being swallowed by Stalin. I could see Poland being THE sore point of Europe for decades.
Germany would regain Ruhr eventually
I don't see it pre-WWII. Just like nobody gives a damn today about will of Crimean or Eastern Ukrainian population, nobody would care about wishes of Ruhr people to rejoin Mother Germany, as soon as the Germany is communist.
Maybe with some luck you could have communism with out the Evil Empire leaders
I don't believe in planned economy long-term, so eventually the system should bomb. However, it might took a lot longer than in OTL.
Might not be a bad place to live.
Comparing to? OTL Soviet Union? Almost certainly (Stalin did rob the country pretty severely to pay for industrialization). OTL pre-WWII Germany? I would say, better for poorest 10% of OTL German population, somewhat close to OTL for middle class, much worse for top 10%.
Not entirely true. As per the Polish-German customs war it is possible to diversify the trade relations, for example by building trade relations with Scandinavia.
This is exactly the mindset I was talking about. Voluntary cancellation of trade with two by far biggest economies of the region, driven by political considerations and augmented by heavy self-hypnosis campaign that puny Scandinavian market is as good as mammoth-sized Russian and German ones.
Please, elaborate. It seems there is some important aspect of OTL that I am not aware of.
IOTL Soviets bought all their tank and tractor producing capacity from American companies. Americans were nice enough to oversee plant construction, equipment installation and training of the Soviet workers. Same for main Soviet car plants (Americans built GAZ from the ground up and supplied equipment to modernize WWI-era Moscow ZIS, equipped Moskvitch car assembly plant and initially supplied car kits for assembly here). Out of 4 main lines of aircraft piston engines, one (of I-16, La-5, Tu-2, Pe-2 fame) goes back to license-built Wright Cyclone, another (powerplant used by Shturmovik and MIG-3) is a BMW VI derivative, third and fourth are based on French designs (Gnome and Hispano-Suiza). Only Beemer engine is not related to Depression-induced fire sale. Most Soviet tanks were of either British (T-26, a.k.a. Vickers 6 ton) or American (BT) design, with original designs being either barely adequate (T-28) or outright failures (T-35). On the top of that, American equipment and cansulting was essential in building of many steel mills, powerplants, aluminium plants etc. Now, this might not happen IATL to the same extent, as a lot of OTL sales had been influenced by barely disguised racist thinking "Russians are too stupid to put the new toys they buy to a good use, so we're earning money without actually helping the Red Devil", and nobody ever questioned abilities of German workers. But, in a Depression-crippled world temptation to trade with Reds who're paying cash would be great.
On the other hand it is possible that Germans would rather emigrate from Communist Germany to the ’Rhenish Republic’, rather than from Ruhr to Soviet Union.
As far as I know, Soviet Union, despite having pretty porous borders in 1920-1935, enjoyed a positive migration balance. Red Germany, not destroyed by civil war, would be pretty attractive to half-starving unemployed workers of Rhur, who would be on receiving end of French occupational regime.