The Siam Huts on Koh Chang Island are a great place to stay if you know what you're getting into. These are very simple 1 room huts that feature a bed, a mosquito net and if you've opted for it, air conditioning. For the money, you also get a private bathroom with shower.
I stayed in the "A" section huts which are about 10 yards from the Gulf of Thailand. The sound of the surf crashing against the shore at night was amazing.
The staff was friendly. There was plenty of food and drink available, including nightly BBQ. On the Saturday night of my stay, there was a big "neighborhood" party with DJs and dancing. On other nights, the staff would show movies (English w/ Thai subtitles) on the big screen under the giant central Lanai.
It rained fairly often during my time on Koh Chang, but that was to be expected for the time I was there. Just be careful as the deck can get incredibly slippery and there are some holes in it.
Overall, the Siam Huts exceeded my expectations. That said, my expectations were for a very rustic hut on the beach for very little money.