We enjoyed walking around the Aloha Tower Marketplace. It was much less busy than the Ala Moana shopping center, although it would be busier when cruiseships are in port.
There are a number of small shops and restaurants that seem to be geared towards tourists. You won't find a lot of high end shops here, but its a good place to pick up some souvenirs, and some shopkeepers will bargain with you.
I wouldn't spend all day here, but its a nice quiet place to do some shopping and spend a couple hours. The tower itself is rather nice. It's not very tall in terms of towers, but its nice.