I was at Caledon Oxbridge last night, and another mentor was demonstrating some of her Mesh avatars. I was impressed by the smoothness of the mesh structure, especially around areas like the corners of the nose and the elbows, where the traditional avatar mesh is "skimpy" and produces distortions. But there was one big problem: no facial movement.
None. The eyes don't blink, the mouth doesn't move. There are no provisions (yet, anyway) in the avatar "bones", the skeleton that distorts the mesh and lets us move, for facial movements. This makes the avatar look rather depressingly like a doll or a statue, instead of a person. We've grown accustomed to even the quite limited facial animation of our avatars, and I don't think many of us are going to be willing to give them up.
At the same time, however, I was gleefully playing with creating and editing big prims. It is SO nice to finally be able to actually build with prims larger than 10 meters, without all the compromises involved in using the limited sizes of pre-made megaprims. This will be a tremendous aid to people like me who build large structures. Thanks, LL!