We didn't stay at Zamas, but we did eat dinner in their restaurant. We left puzzled at why there is so much hype about this place.
The food was mediocre, and overpriced. The ambience is fine, but the restaurant is very large in the sense that it seats many people. I prefer the more intimate experience found at most other restaurants on the beach.
We weren't impressed with the service, either. Our waiter brought my husband a dish he didn't order, and gave us an "Are you crazy?" look when we asked for the correct dish. I understand that you shouldn't expect the same customer service that you get in the US while in Latin American countries, but if you cater to tourists and charge US prices, then you should prepared to provide US customer service. (This isn't an ignorant comment, even my Argentinian husband agrees that customer service really doesn't exist in Latin America).
I definitely would not go back. There are so many other better places both in Tulum town and Tulum beach.