First, vacancy rates at many centers are quite low but unfortunately vacancy is becoming a poor metric to measure the health of a single shopping center or a portfolio of them. Many centers are very quiet and at those where foot traffic is decent there are not a lot of shopping bags to be seen.
Often, particularly in upscale lifestyle centers, only the restaurants are doing a brisk trade. In many cases occupancy is being kept artificially high by (a) rent relief and (b) the cost to retailers of early lease termination.
Second, everyone is in everyone else's business. This is not new but it has evolved to the point where it is very difficult to distinguish between retailer categories. For example, drug stores such as CVS and Rite-Aid now typically devote an entire aisle to booze, with hard liquor on one side and wine on the other. Then there are the dollar stores that have a couple of aisles of supermarket-type products, a fresh produce section and a dairy fridge.
Third, what the U.S. doesn't need is another luxury shopping mall but now it's got one, in Las Vegas with the opening of Crystals at CityCenter. The interior and exterior design are impressive (although there are some who disagree with me on that) but the brands are the same old and no one seems to be doing any shopping there. The mall is primarily, at the moment at least, a place to gawk at and a backdrop for tourist photos.
Fourth, US supermarkets are still possibly as much as a decade ahead of their Australian counterparts with respect to presentation, price and assortment. This is a sad comment given the opportunity Woolworths in particular has had to catch up to the rest of the world during its period of dominance in Australia.
Fifth, Costco is now in or near a very significant number of shopping centers but its degree of connectedness to the centers is highly variable. For example, at Lakewood Mall in Los Angeles its entrance is quite adjacent to that of the mall proper. At Paradise Valley in Phoenix it turns its back on the mall as though in contempt. Australian shopping center owners will have an interesting puzzle to solve to integrate Costco in a way that maximises cross-traffic to the main mall while not interfering with Costco's successful model of insularity.
Sixth, the most busy and happening shopping center I saw in any of the three cities was Desert Sky Mall in Phoenix, which has done a great job remerchandising for its local Hispanic demographics. This is a great example of how differentiation through addressing a genuine market need can produce a much better outcome than simply bringing in the biggest names in retail you can lay your hands on. (By the way, the center looks a bit shabby, as though it's seen better days, but that didn't seem to bother the shoppers.)
Seventh, best new urbanist development in the three metro areas is still Kierland Commons in Scottsdale. The Grove and Americana in LA are also still pretty good, and there is a newish one in Las Vegas called Town Square Las Vegas which is nice too.