No one expected that, except some loony lefties!
Not true. That's how the reunification (and later the so-called "Solidaritätszuschlag") was sold to the people of West Germany, and don't forget that the GDR was one of the most developed countries of the Warsaw Pact. Industrial pollution was the norm, but nobody expected to find whole districts that were completely ruined by the chemical industry for example. The commies were very good at hiding their skeletons in the closet.
He certainly wasn't
Come on, why do you think he had the nickname "Birne"? In German, that wasn't only a reference to his physical stature, but also a mockery of "his provincial background and simple language"
He did not make the reunification possible,
What I meant is something else. He was clever enough to use diplomacy and personal bonds in his favor and to the advantage of Germany. Kohl was a good friend of Gorbatchov at that time, which made things a lot easier.