Those are two different things... all countries and economies are compatible with Marxist thought, in fact Capitalism is crucially important to Marxism in its role to create an industrial base to allow mass production and urbanization at the cost of generating a proletarian class out of the once agrarian workers.
However states that describe themselves as Socialist in their constitutions have made some good policies, your question permits me to list ANY working policy in those countries, not just the economic ones.
There are lots of good policies, but it depends on what your viewpoint is, from their perspective and knowledge I would say that the USSR's instatement of Puppet Regimes in Eastern Europe was a good policy from their POV (mainly the history of having few allies, being invaded by the west, and having little say in international affairs), but not a good policy from the Western POV. From even a Western POV, I would give good grades to most of the Asian Officially Socialist Countries for trying to increase the rights of women where historically there has been few.
In terms of Economics, that is more difficult to pin down, because Economics is the study of scarcity and the resolvement of the issue of scarcity, and failing solving it, explaining the rules behind it and making the system of trade of goods sensible and efficient. So a good economic policy is heavily open-ended, and wide to interpretation on the qualitative value of it.
If I suggest that their focus on industrialization was a good policy for allowing a larger output of goods, increasing urbanization, and increasing the Human Capital by a more educated society, one could suggest that with the larger output of goods it just lowered the quality of the individual good, the increased urbanization did little because it drew workers away from the production of food, and the increased education was counter-beneficial because it took funds from the government to invest in projects like making sure every home had electricity even in the most rural areas.