Hi David
I dived in the Gilis in March.
There are, as you probably know, 3 Gillis. Trawangan is the busiest, Air much quieter (where I stayed). I didn't visit Meno. I dived with an operator, Dream Divers, off Gili Air. Diving was from large canoe-style boats with outriggers. The operation was good, dive briefings simple but sufficient and the guides pretty good. I did think you needed a guide for a number of the sites where quite long drifts across sand ridges were involved. The diving from all three islands was on the same locations. Dive times were all over 60 minutes.
Visibility was extremely good - in the 30m range. The water was incredibly blue! Temperature 30C at depth. Marine life was sparse although one or two sites did have reef sharks dozing on the sand. Some had turtles. Of the 7 dives I did, a number of the dives were relatively deep at around 30-35mm. The rest in the 20m range. Reef structures tended to be patch corals on white sand. There were some nice Gorgonians which were good to shoot against starbursts.
The diving was enjoyable and Gili Air a very relaxing place to visit. I travelled by ferry from Lombok to the Gilis; and then used a local ferry canoe to get to Trawangan from Air and then the Gili Cat to Bali which was very good and easy.
I wouldn't want to make a special journey to dive the Gilis but I was also visiting Tulumben and was working in Lembeh so was in the neighbourhood and, as such, it was well worthwhile. I used a Tokina 10-17mm lens on almost every dive and thought it the right choice.