This is probably one of the best restaurants I've ever been to anywhere. It's a short Tuk Tuk ride from Long Beach and it's probably too difficult to find the first time without knowing, as it's well off the main road. If you ride there yourself, make sure you go from the north as Google Maps took me a really dodgy way through a muddy path.
When I was there in 2012, it was top of the Tripadvisor list for the whole island and it definitely deserved it. I've now been there six times. Their special is fish with coconut curry - and they let you choose your fish from a plate that day's catch. The curry will blow your mind (hopefully). I recommend getting a pot of the sauce to go with it as you don't get enough. If you're not sure how spicy to get it, then get medium with the fish and make the pot spicy (the spicy version is much better). I also recommend the shrimps in sticky garlic sauce. I could eat those two dishes every week and be very happy!
It's more expensive than most Thai food but it's definitely worth it. Getting there after 7pm means it will be busy and you might have to wait for a table.