I think that Mk 1 and Mk 2 had the darkest feel of all the games. This is due partly to the fact that the series was still really new, but I think it had to do with the stage designs too. Mk 1 had the Pit, which we all remember had dead bodies and severed heads at the bottom, and it had you fighting at night with a pitch black sky and full moon. Not to mention the killer fatality you could do if you won the match. Mk 2 had the Pit II, which also had you fighting at night. The Pit II also had one of the most realistic fatalities ever to appear in a Mortal Kombat game (when I say realistic I mean something similar could happen if someone were to fall from a great height.) Almost every stage in MK2 used dark colors. The Dead Pool used dark green acid, the armory used black and bright yellowish/red and had weapons in the background, the Kombat Tomb had the skulls and the dark red sky, and the Wastelands had the dark purples, blacks, and the impaled victims in the background. I think that all Mk6 needs to do to make the game feel dark visually when you are playing it is to add darker colors into the backgrounds of the stages and include stage fatalities so that we get the feeling of danger down below (if you're on a bridge or platform). And to make the stages simplistic so they are believable, but also include some depth to the stages to ehance the fighting experience. What do I mean by that? Well the Pit I was very simplistic, but the colors in the stage gave it an ominous feel, and you always loved it when you got to fight there because of the killer fatality you could do at the end of the match. Same with the Pit II. These fatalities were a lot more believable than some of the fatalities that came after it in mk3 and beyond, and that's what made them so good and gave the earlier Mk's that dark feel. (sorry about the spacing. I edited my message and it got messed up)