Cabanas Copal is set right on the Caribbean and consists of about 45 cabanas, a bar, and a restaurant. We stayed in a sea-view king suite, which was directly on the ocean (down about 10 steps to the beach).
The cabanas are close together and small, but it was exactly what we were wanting. We spent our time outside, and really only slept and showered in the cabana. No electricity, but we had hot showers. It was definitely rustic--thatch huts with concrete floors, but very clean and no sound except the ocean at night. It was about three steps up from sleeping. If you're looking for the party at cancun, this is not the place. But we met lots of other couples and had drinks and partied 35-year-old-style and went to bed pretty early. My fiancee was up every morning at 7:30 and did the free yoga classes, and I went for a run. There are tons of resorts with better restaurants within a 10-minute walk, and Tulum was a $2 cab ride, where there are many local restaurants. If you like something quiet, beautiful, and about two steps above camping, then you'd love this place.