I had high hopes for the DLC, but so far it has been lackluster. Skarlet I hated at first, but the more I use her, I think she is a solid, original character (even if she was borrowed from Kira/Nitara). Kenshi and Rain have yet to impress me much. The roster was fine upon release and now I think it's getting a little bloated. I would actually go far as to say the fourth character is unnecessary.
Rather than OD'ing on more skins and characters, I would like to see more arenas added. Namely: The Warrior Shrine, The Kombat Tomb (with fatality), The Portal, The Pit 3 (with fatality), and add in the fatality for The Bell Tower. I also play with the idea of The Pit II in the sense of the original fatality versus the hybrid of The Pit and The Pit II they did. Incorporate the X-Ray on that somehow and it could be impressively brutal.
Overall though, the DLC is not terribly expensive ($20 for all four characters, $15 if you bought the season pass) and most of it's free, so in all honesty, there isn't all that much to complain and whine about.