You must, must go.
Run, don't walk.
It has been vastly improved since it's last incarnation, with more space and light, along with additional rooms and art on display. There is lots (and I mean lots) of Tiffany art, including beautiful stained glass windows, a fountain, paintings, and columns. The old courtyard has been leveled and contains several more sculptures, and there is more space to walk around comfortably.
Inside the old stone bank entrance facade, I lost count of how many beautiful period rooms we walked through. Most of them are replicas of rooms found in homes of the wealthy from the nineteenth century, and they are mind-blowingly ornate and luxurious. There is also a room designed by Frank Lloyd Wright and, on the third floor, there are rooms from Colonial America.
The improvements go beyond the aesthetic. Several of the rooms have electronic touch screens that contain silhouettes of the rooms and you can get more info on the various objects on display in the rooms.
One thing I really love (and the Met has this in the new Greek and Roman Galleries as well) is visible storage -- vast spaces with various objects stored in long glass cases. This is stuff that the museum owns, and are of the period, but that aren't part of any one particular exhibit. The visible storage area here includes a vast array of American decorative china, glass ware, tea and coffee services, tables, chairs, dressers, wardrobes, book cases, sofas, vases, etc. It's definitely worth checking out.
Mr NYC officially gives the new American wing a big thumbs up.
P.S. I have fond memories of going to the American wing as a child with my mother so it was like a rite of passage to go to the new and improved American wing with my wife. Plus ca change ...