AT&T is regularly criticized for having some network issues in cities like New York City and San Francisco, but without a T-Mobile acquisition, the carrier would face even more problems. AT&T CEO Ralph de la Vega has told CNN that one of the big reasons for their purchase of T-Mobile "was the need for additional spectrum" and that, without T-Mo, ATT would run into big challenges in the short term, especially in major cities.
On another AT&T-Mobile related note, de la Vega told IntoMobile that T-Mobile will keep its current pricing structure, although he didn't divulge any more details and no one is quite sure what he meant. The current speculation is that either ATT will keep T-Mo around as a separate arm of the company or that ATT will adapt its pricing to match T-Mo's, although the latter is highly unlikely.
When the AT&T-Mobile deal was announced, ATT explained that the additional spectrum will provide improved service as well as the ability to roll LTE coverage out to 46.5 million more Americans, especially those in rural areas. That should please folks that have had issues with ATT service in major markets in the past, although it's probably not enough to make believers out of the people that are unhappy with the deal.