Well, the original Arma was really clunky, and while some people do like to say "the clunkier it is, the more realistic it is", I really don't find it as hard to move in real life as I do in Arma 2.
Yes, the movement is a bit more like a regular FPS, but that's only because they've made it not a major pain in the ass.
That said, the mousewheel menu is still there, but they've made efforts to make the interface a wee bit better, such as "g" to throw grenade and grenade throwing not being herpderp anymore.
So, movement is more fluid and more flexible in what you can do.
Other than that, at the moment I've mostly seen revamped graphics, which is not really what I wanted. Having tried to do a few missions, all my ideas get shot down by AI that is incapable of doing something as simple as dropping off a few troops. Heck, apparently it's hard as hell to get a mixed-vehicle convoy going in A2... and it's not changed so far in A3.
I get that the graphics could be better, and it's amazing that they're so much better without a huge impact on performance, but as a DF player, I value mechanics and features more than graphics. I loved it at start, now I'm starting to get anxious about whether or not they'll fix what I feel is more important.