We've recently returned from our 3rd trip to Lady Elliot Is with our 16 & 14yo girls, and it definitely won't be the last. September is our favourite time I think - still whales about (we saw some every day off shore), Mantas, baby birds haven't hatched yet, and waters are calmer and warmer.
This island is not (nor does it claim to be) a fancy resort where you watch your toenails dry, get waited on hand and foot, or sit by a massive pool with your cocktail. Instead, it is so much better - lots of snorkelling spots depending on the tide (you can only snorkel the lagoon a few hours either side of high tide, so consider this if on a day trip), BUT the Lighthouse and Coral Gardens are fantastic and you can go without a tour. Our activities revolved around: joining a snorkel safari (Mantas, turtles), Glass Bottom Boat + snorkel (more turtles, huge amount of coral fish): joining the excellent educational free walks (Behind the Scenes, Bird Life, History, Geology), getting up early to watch the sunrise etc. I didn't dive this time, but my partner did and got to dive on the rare eastern side off the lagoon (often very strong currents so closed) and absolutely was spellbound by the huge table corals and sea life. I didn't miss out at all, snorkelling with the kids several times a day. The staff were so wonderful and passionate about their job, and it rubbed off on us all. The food was varied and plentiful as usual, with the kitchen and bar staff all so friendly.
I love that the staff are obviously treated well enough to keep them returning time and time again - they eat the same food and always ready with a friendly smile. No subservience, just true professionalism.
Our 2bdr Beachfront Apartment #1 had the best view yet, and the upgrades to the bathrooms are great. The little bar fridge came in handy for some byo snacks etc and the bar happily provided some ice and tonic. I had no problems at all drinking the desalinated water (as per some other comments), and I'm quite fussy.
Overall, we just adore this place and love what the custodians are doing to regenerate the greenery on the island itself. Underwater is always a treat for the senses. We will be back.

3rd visit and has only got better. Lots of mantas, turtles, shark, etc. The guide lines are great when moving against the current. A drink at sunset after the last snorkel at lighthouse beach watching the whales move past is unforgettable.

Absolutely amazing place - the island, the nature, the staff and the accommodation. Almost impossible to find a fault. From the moment we were picked up at Redcliffe Airport to the time we left everything was amazing. We will definitely return one day. If you are looking at the Beachfront Units BF3 has the best aspect plus the bonus of front and rear balconies!! Ref Units 8&9 have the best views of the lagoon.