We enjoyed this part of Lisbon very much (together with Baixa, hard to see where one ends and the other one starts anyways).
There are several streets which are enjoyable. Countless restaurants, bakeries, chains and independent stores.
Besides Rua Augusta and its side streets the Rua Garrett is surely worth checking out. Like mentioned in another reviews, the restaurants on Rua Augusta are good for drinks and people-watching, but I would avoid eating here. Menu, quality and value are just not good enough.... but there is lots of good food in this city.
Rossio and the Praca Do Comercio are surely other must-dos. But make sure to walk along the smaller streets in the west of Chiado too (close to Bairro Alto), lots of charm here!
Some of the parallell streets to Rua Augusta get pretty quiet at night. Nothing scary, but not much to see or do though.
From some angles you also can get nice views of the Castelo, especially at night a colorful sight! read more