FWIW, I've just played the alpha for an hour and frankly it's in better shape than Arma 1 or 2 were on release. Granted there are lots of things currently not in there (alpha, not feature complete), but what they DO have seems to be working well. The SCUBA stuff is awesome.
Vehicle physics now uses PhysX and they move logically now. No more "skating on ice that appears to be a grassy hillside".
Oh, and unlike both Arma 1 and 2, it runs smoother. My current PC (i7-2600k and GTX570, neither OC'd) is arguably older than my setups at the time of those releases, and they ran slower and more choppy then.