We stayed two weeks at Gina's place and had an amazing time. The island is incredibly beautiful and we would definitely recommend hiring a car for some/all of your trip (although the buses also work well for the odd day). My husband wanted a very specific car so we didn't actually hire from the building and benefit from the reduced-fee parking. We did manage most days, but parking is super difficult to find on the streets nearby, so bear this in mind.
As other guests have said, the views from the apartment are stunning and really make it special. Sunrise is particularly beautiful. It's in a great location for getting down to the beach or to the shops, but there are also some handy places nearby if you don't feel like walking. We especially liked Cheese Burger across the road (good value), and the bakery in the lobby. The pool area is also nice for relaxing and has a couple of BBQs.
On the whole I would say that the food was more expensive than expected in Hawaii (though obviously it depends what you like to eat), so you might want to factor this in to your budget, especially if you're staying for a while. Loads of places do happy hours so that's a bonus.
We did so many amazing things on our trip - swam with dolphins, hiked in the mountains, snorkelled at Hanauma Bay, drove an ATV through Kualoa Ranch. We would recommend it all. There are so many things to do, it's worth getting out there and exploring (plus, the beaches are much quieter away from Waikiki).
We couldn't have asked for a better holiday!