The best island we visited...
When we headed for Koh Pha Ngan, we feared that we'd be greeted with hordes of tourists clogging up the beaches and rampaging through the nightclubs. And, while it is still a tourist-oriented island, it was actually one of the places what we most enjoyed during out trip through the islands.
To visit the island, I recommend renting a scooter (the island is full of rental places) and explore the less-visited cliffs, jungles, and beaches away from the tourist centers. I'd also recommend hiring a tour to the Mu Ko An Thong Natural Park and see some of the virgin beaches and go snorkeling in the reefs.