Gangga island resort is top notch both landside and divewise, never had such comfortable conditions for diving : I had my own diveguide and never had anything to worry about my camera nor my equipment. Gaspare the resort's owner inputs european finesse and italian warmth in the hotel management, they also try to provide elaborate food and do as much a they can, even sometimes it's a hit or miss.
The wooden bungalows are very comfortable compared to what I've seen around, they're even too westernized for such a place, powerful A/C and no bugs indeed!
I can heartfully recommend the place although it is NOT located on Bunaken but on Bangka area, which is viewed from my side even better. If you're looking strictly for Bunaken, then you should go to Siladen resort in the same comfort range.
Bangka is halfway between Bunaken and Lembeh and from its strategic location, you can dive the three areas. Lots of resorts tend to forget Bangka though I think it is even more worth the dive than Bunaken (I wouldn't exchange a Sahaung, Batu Mandi or Paradise Pier dive against any Bunaken dive).
I suggest you book through Manado Safaris travel agency, which is very reliable an efficient. Jeremy the owner (ex-KBR manager, now a long established travel agency in Manado) often offers promotions.
For some Bangka area UWphotos, you can click on the gallery link embedded in my signature, there's a Bangka/Lembeh subgallery dived exclusively with Gangga divers.