Wonderful stay at Heron Island! Snorkeling and diving were excellent! The naturalists/guides were super informative and engaging. I-spy boat worth it, especially if you have anyone in your group not interested in snorkeling. If it’s a clear day, you will see lots of fish and coral. Food in the restaurant was really good, plenty of variety, good portions, friendly staff. (Prices comparable to good restaurants elsewhere.) Espresso drinks and cocktails at the bar were tasty! Room was clean, beds were comfy, extra blankets available in case you get chilly.
We did end up spending an extra day because a storm rolled in earlier than expected and the ferry out was cancelled. But, the reception folks were great at getting us situated back in a room and arranging a helicopter ride out as soon as possible. (Far more expensive than the ferry, just a heads up.)
Good to book your activities early, before you arrive on the island. Sign up for the walks and talks when you get there - some limit the number of participants, and the guides are awesome, so definitely worth joining in if you can. Bring a good book in case it rains. Make sure your plans after have some flexibility in case the weather turns and you have to stay an extra day or more. We went end of July, not crowded at all, really pleasant temperature. Planned three nights, which was plenty to do everything we wanted.