I think this is a good question, and shouldn't be down voted. I have a couple of thoughts.
My understanding is that dialectical materialism is a concept most associated with Stalin, Lenin and Lukacs. It was advanced as a kind of official Soviet interpretation of Marx's thought.
Lenin is pretty much of a third rate thinker but compared with Stalin he's a genius. Lukacs is actually pretty worthwhile in general. If you want to think about the concept in more detail I think you probably would have to go to the source, rather than listening to my approximate recollections.
I think basically it's that he (Lenin) thinks of dialectical materialism as like the scientific method of Marxism.
To me this is so disagreeable as to be not worth engaging with, because, to start with, the dialectic isn't supposed to be a 'method', it's the structure of reality according to Hegel, not just a style of argumentation. So I guess I would say that it strikes me as extremely bad, since it doesn't do justice to what the dialectic actually is (assuming you care about this).
Compared with just "materialism", or "historical materialism", which are the terms Marx (and other interpreters of Marx) would use, it seemed to me (when I last read anything dealing with it) really clunky and simplistic. Though there is definitely more to it than what I've hesitatingly outlined.
I'm hoping that someone with a higher level of investment in this stuff can pitch in, because I've forgotten most of what I've read about this and what I've written above is probably too simple, and possibly wrong about some things.
Hope that's somewhat helpful.
