Has anyone vacationed on the island of Ko Sumai, Thailand?

My husband and I are planning a trip to Thailand and want to spend most of the time on one of the beautiful islands. I know practically nothing about Thailand but my husband lived in and around Bangkok for 2 years. He said that a lot of people vacation on Ko Sumai and that that's where we should go. But from what I've seen its not very private. It seems like everyone goes there. I am looking for something a little more secluded and peaceful. But I'm definitely still interested in hearing about it. If you have stayed there what was your experience like? Would you go there again? What hotel/resort/bungalow place did you stay at? How expensive was it? What was your favorite parts? What would you not do again while there?