I have been to Giens in the past many times - so I knew what to expect. My wife and I stayed in the Domaine de la mer for three nights in August 2008. Giens in general is a beautiful island and not so touristic as other parts of the Cote d'azur. Hower, if you go there in July/August the beaches are crowded by french holidaymakers. Be prepared to get stuck in a traffic jam whereever you drive during that period - even on Giens.
The Domaine de la mer is situated in a beatiful vast area with pine trees and direct access to the sea. It mainly consists of appartements and bungalows for self catering - the french love that... We stayed in one of the few nice hotel rooms which are meticiously clean and in a good standard. The "design hotel look" is "Ikea"-like design but that's still much bettern than shabby furniture. Altogether very pleasant rooms.
The pool is fairly small and crowded by hordes of children and their parents for the whole day. But who needs a pool when the sea is there?
Restaurant: breakfast not included in the room rate, buffet with good choice. Dinner: fairly small menu, we liked the food - but it's overpriced. We did it once as the view from the restaurant's terrace over the bay at sunset is amazing. Better drive to Port d'Hyere - there are numerous restaurant for all different moneybags.
In general, I would always go back - being aware that in Southern France they "take it easy" - which is nice but also meaning that in many cases everything is a bit neglected, and locals / staff hardly speak any foreign language. So better train your french language skills... ;-)