When I went back to Koh Phanganafter 5 years "absence", I was pleased to see that, despite the full moon party, which I detest, and the growing popularity of its neighbor, Koh Samui, the island of Koh Phangan has remained an island which has resisted the urge to cover everything in concrete.
If you just want to relax on holiday, then you'll find the north of the island peaceful. The south is where they have the full moon party, (and the other similar parties). I stayed in a small haven of peace on the beach at Haad Salad. It's a small beach where I can relax, looking at the most beautiful sunsets in Thailand, having massages - a perfect holiday.
But as I get bored of doing nothing after a while, I got on my scooter and went off to explore the island more thoroughly. In the north there is the bay with the fishing villages (and the great restaurants which go with them). Not far from there I embarked on an upwards pathway, followed by steps, which led to a bar/hotel (more tents, really) clinging to the hill but with a marvelous view. Lost in the middle of the island were a Chinese temple, some waterfalls and another viewpoint. If you are feeling really keen you can get to the isolated beaches on the east of the island, but be careful because the roads are in a very bad state in that area.
During a trip to Thailand, there is always the question of which island to choose to go sunbathing. Andaman Sea side? Gulf of Thailand side? If you have time my advice is to choose one island on each side. In the Gulf of Thailand I went to Ko Pha Ngan.
The island is small, wild, and has very varied countryside. It's the ideal choice for both breathtaking beaches and walking on lost trails. Visitors who want tranquility (relatively speaking) will head for the wildest beaches in the north, surrounded by coconut groves. Party animals will head south, especially during the Full Moon Party. Whatever your choice, I suggest you rent a snorkel and do a bit of snorkeling. There's no need to go too far from the shore. The sea bottoms are wonderful. There are a multitude of multicolored fish in the coral, which makes you feel like you are diving in an aquarium. I was even lucky enough to see a mermaid among the sea cucumbers. Oops, no,sorry - that's my wife swimming with some German tourists!