It's a little weird that people rag on it for being slow (I remember that being a complain in its day even) because DD should be slow and heavy, not really fast and probably not combo'riffic. Very deliberate hits (with a mastery of timed supermoves starting with DD2,) very clear understanding of what enemy type you're facing and what weapons are on the playfield, that's kind of what I think of as DD gameplay.
Maybe the godfather, although the grandfather would probably be considered Renegade (also by Technos.)
Kind of a clumsy early bralwer (and I don't remember it porting well,) but one innovation in Renegade I regret being left behind by most beat-em-ups was the Renegade wall-jumpkick. Brilliant use of space, every beat-em-up should have wall-based attack/positioning techniques.