Hello,
I've been there for 10 days in 2004 and I absolutely loved it; it's a total dream.
We stayed at an oceanfront "premium bungalow", that was like having your own private beach house (without a kitchen), with a huge swimming pool all around and underneath it. All very quiet and private.
If you are looking for a lots of activities and fun, that's not the place. What you get at Nannai is relaxation, good massages, excellent food, peace and quiet.
The service is superb: a fresh fruit plate every day (not only upon arrival), excursion arrangements, beach service, etc.
The food is also very good; breakfast, afternoon snacks and dinner are included.
The town of Porto de Galinhas is a lot like the North Shore of Oahu, with surfers, tourists and locals all mixed. It's not within walking distance from the hotel, but they can arrange a taxi for you, that waits for you and brings you back hours later for maybe 20 dollars.
There are restaurants of all categories and cuisines.

Nannai is typically a place for couples/honeymooners, without many kids, but it all worked very well with our then 8-month old, because we could be outside in the sun while he was inside sleeping in an A/C room.
For those seeking a family resort in that area, I'd suggest Summerville (just next door to Nannai), or renting a vacation house. Most houses there include a cook/cleaning lady and another housekeeper.