I haven't thought too much about the new AT&T logo, but after seeing it online so much lately, I finally figured out what went terribly wrong: It looks bad scaled down.
As you can see, the subtle, dark blue lines that swirl against the lighter blue swirl, creates the effect that the entire logo is pixilated and very lo-res.
The problem could be fixed if there was a greater contrast between the two blue colors. Unfortunately for AT&T, this is likely going to create a terrible lo-fi look-and-feel for many other people too, even when not conscious of it. A company like AT&T should have a very sharp, crisp and fine logo, not a crappy, pixilated, 1996 looking one.