The first characteristic, in most Eastern Bloc countries, was the violent nature of the takeover. After being overrun by German armies, the countries were again overrun by their liberating comrades in the Russian army. A relatively immediate and forceful government takeover of nearly all aspects of life followed. Remember that this is not just socialism, it is communism, so the government controls not just the means of production, factories, farms, etc., they also control any product coming out of those producing enterprises as well.
The state quickly became an overwhelming force in people's lives. Religion was not allowed in many of the Eastern Bloc countries, travel and freedoms of most kinds were restricted, and social mobility was reduced even further. There were pogroms in many Eastern European countries where those whom Stalin saw as being possible resistors to his agenda were killed by the millions.
Some countries were not quite as severely restricted, Yugoslavia was one, but in general, most of the Eastern Bloc disappeared behind the Iron Curtain.