There is only one dive operation there: http://miguelsdiving.com/. It can take up to 8 underwater photographers on the boat.
Most of the dives are wall dives and they do have some sites to offer muck diving. Gorontalo seems more popular for macro subjects due in part to the book bearing the same name. The reefs are pristine and cover with dense corals formation. This is possibly due to the short season from Nov - April in addition to the fact that there is only one dive op. Visibility averages about 20m and water is warm at about 27-29 degrees Celsius.
Sponges are pretty much everywhere in varied shapes and sizes. One of the main attraction would be the Salvador Dali sponge with its unique current swept texture (Pic 2).
Out of the five diving days, I was using wide angle lens for 4 days. I can't comment much on the macro subjects which it is popular for. There are some endemic species like the Blue Belly Blenny which I find absolutely beautiful. However, I had my fisheye lens on the camera at the time when it was shown to me, thus couldnâ€™t share it with you.
You can check out the web site of the dive op to have a feel of what you can expect to see.
One thing that is a bit of a 'pain' is the travel to get there. There are 3 options: 1) Fly in to Jakarta to transfer to a domestic flight (about 5 hours) via Makassar (short stopover) to Gorontalo 2) Fly to Manado, where you can do some dives and take a road trip about 8 hours to get there or 3) Take a domestic flight from Manado (about an hour if I am not wrong) to Gorontalo. The issue with this last option is that the domestic flight schedule are less certain and less frequent which makes planning troublesome.
I took the Jakarta route. My flight to Jakarta is at 9:05 am and by the time I reached Gorontalo and stepped into the hotel, it is about 10 pm. I was rather 'stoned' by then.