The TOS (and the transparency of the devteam), first (and second) and foremost, although that isn't a down and dirty functionality thing, obviously.
OpenID's really well integrated, I like the setup of following (you can choose to give people post access without following what they post, for instance. Following and being followed are separate entities, and aren't as intertwined as friending on LJ/IJ/etc.) It probably helps that I have some LJ friends who were real DW early adopters, and I've gotten to pay attention to their thoughts on the site as they were going through it. I've really only used it myself for reading and mostly commenting thus far, but what I've used it for, I've liked.
Do I like having oodles and oodles of icons? Sure, although it's not the high priority for me as it is for you, so your mileage, of course, may vary. Which is the point of discussion in the first place. XD