We stayed for 3 nights before heading forward to Chaweng. Three words: everything was perfect.
Clean and well-maintained room with all the amenities you could possibly ask for. Kind and service-oriented staff, the scent of the Jasmine flower everywhere, spacious pool, sunset by the beach, massage on the beach, etc. It's a perfect, serene and romantic get-away.
However, if you're looking for wild parties and Khao-San-Road-like-markets, this is not the place. We rented a scooter from the hotel (250THB/day) and rode to Nathon, Lamai beach, and the nearby surroundings. That's how we explored that part of the island.
When going back to Koh Samui (whenever that'll be,) we'll definitely stay at the Sunset beach resort again.