The Aria isn't as nice as the Cosmopolitan, but Hotwire calls it 5 star. The rooms seem small for a 5 star hotel. The service is excellent and the pool(s) and gym are wonderful. Because Javier's opened in the Aria, they now have a really good dining option.
I like being near LV Center just to walk around and get out of the "Vegas scene". I'd definitely stay here again, though the casino doesn't rate with the Venetian, Caesar's or the Wynn.