If you love snorkeling, you MUST stay here. Sai Daeng occupies a peninsula that has what may be the best reefs in Koh Tao. This is where the dive and snorkeling boats come, but YOU can stay here. The rooms are comfortable and the views are amazing. The included breakfast is excellent. After breakfast, just head for the water (on either side of the peninsula) and enjoy the fish, turtles, rays, coral, and all sorts of interesting sea creatures. The water on the north side was always clear, the water on the south side can get a little cloudy when the wind comes up. This beats "off the beach" snorkeling I've done anywhere else in Thailand, Hawaii, Florida, Bali, etc. So much easier not to have to take a boat somewhere.
The food at the resort is excellent, but it's Thai food (which I love, but I'm just saying....). The staff is friendly and helpful. The place is remote from the town. If you're not on a motorbike you will be dependent on the shuttle and taxis. I found no need to leave the resort at all during the 8 days I spent there (I extended twice, I couldn't leave). This was certainly the best snorkeling experience of my life. If you love to snorkel, whatever you need to do, spend a week at Sai Daeng. You won't be sorry.
One warning. The peninsula is on a hill. You WILL need to be climbing steps. If you have problems walking, you'll have to skip this. I'm 74. It wasn't a problem for me, just good exercise. But it might be difficult for some.