The exhibit itself is not spectacular. Although it is naturalistic, each of the two main spaces are fairly small. Plus, they have a small viewing line and make people move constantly to keep the line going, so you can't just sit and watch them. For all the money they spent on it, not a very good setup (but then again they have had several cubs, so maybe off-exhibit breeding areas took priority over public viewing).
As others have said on this forum, National Zoo in DC is the place to go for best U.S. panda viewing.