Leninism, Stalinism, etc. (countries you mentioned) are attempts to fix problems with capitalism identified by Marx and Engels.

Marxism is a method of socioeconomic analysis and it true that Marx and Engels writing offered scientific/philosophic background for revolutions (which ended up worse than capitalism). But their critique of capitalism is still very much valid.

If you want be successful capitalist you need read "Das Capital": many things will become clear. Or just watch it: http://davidharvey.org/reading-capital/