To me the shocking thing about the collapse of the Eastern Bloc (both at the time and in hindsight) was that it was nearly bloodless, with events in Yugoslavia and Romania showing what easily might have been the outcome everywhere. Once it became clear that Gorbachev would not send tanks to reinforce fraternal bonds with the various people's republics, the wheels came off rapidly. But it would be hard to overstate the level of surprise in the region, where memories of 1956 (the invasion of Hungary), 1968 (Czechoslovakia), and 1981 (Poland [1]) were very much top of mind. It was simply expected that attempting to break with Moscow would result in a military crackdown.

I think subsequent events have proven that Soviet Russia had the capacity to retain at least some of its empire by force, especially if they coupled that with a de facto return to a market economy, the course that worked so well in China. But to his credit Gorbachev decided not to send in troops, and the coup that resulted was too ineptly planned to stick. Gorbachev was a complicated man, certainly no saint, but the decision to let the Soviet empire go merits him a statue or two.

[1] The Solidarity movement in Poland in 1981 was suppressed by the Polish army without foreign involvement, but the military junta all but said that the alternative was a Soviet invasion. Whether or not this is true is actively debated in Polish historiography, but was universally believed at the time.