Here’s a nice history of the decades old relationship: https://www.dw.com/en/russian-gas-in-germany-a-complicated-5...

It was a major success, contributing to the thawing of relationships with the Soviet Union and probably contributed to the peaceful end of the Soviet Union. It supported several EU countries through their economic development and kept the EU afloat through the financial crisis.

It was a very important source of energy and there is no replacement. This can be seen by the flight of capital, deindustrialisation and poor economic prospects in Germany and the EU.

But as far as I know, many countries still import energy from Russia, either directly or laundered through third parties.