While we greatly enjoyed Koh Kradan - quite secluded and underwater was beautiful, I must say that we were quite disappointed with the hotel.
It's quite run down with many of beach sunbeds already eaten up by termites and mattress covers discoloured and stained. There were many ants and insects inside of our bedroom, some of which somehow managed to get inside of mosquito nets... The bathroom is open-air, meaning we had to take a shower before the sunset, otherwise you invite all sorts of insects. Swimming pool was very small and water was always very hot and murky. I got a massage once and the experience was terrible. The masseuse was okay, but their massage parlour was in a really bad shape - dirty, unorganised etc...
A bit expensive for this kind of standard... Yes, it's the best accommodation in Koh Kradan, but compared to facilities in other places in Bangkok, we thought they charged us too much especially for the airport transportation and dinner.
We spent 8 nights there, but probably 2 nights would have been sufficient. Make sure you choose one of the beach bungalows, not the standard accommodation, which is in a worse state.