The new idle/standing animation generally looks less natural and seems to affect the way the rest of the standing animations look as well. In my quest to restore it to the pre-3.0 animation, I discovered that I also cannot seem to replace the idle animation, period.
It has also been retroactively applied to 2.0 avatars, changing their general feel in an undesirable way. The animations and feel of using older 2.0 avatars should be preserved as much as possible, and for the most part this seems to be the case at least for crouching and prone.