Aulani is AMAZING. We went last year and are going again next year. I was basically planning the next trip before we even left. For what it's worth, we LOVE Hawaii and had already been there a few times before going to Aulani.
You can easily spend your whole time at the resort, but particularly if you are a Hawaii first-timer, you will enjoy having a rental car on hand, especially if you are staying in a villa and will have a kitchen. There's also restaurants off property that are within walking distance.
The Aulani food is good; AMA AMA has really incredible beach views. We ate there three times, hahaha. The kids loved the character breakfast.
Splurge for a partial or full ocean view if you can swing it.
The spa is glorious. If you are a person who does spa treatments, do not miss it.