Been several years since my last trip there. I stayed at the Palace Resorts, which were all-inclusive, so all meals were free. Pretty good food, but nothing special.
The absolute best food I remember eating was during our trip to Chichen Itza in the early 90's. We stayed two days at one of the local hotels right near the back entrance. Next door was a restaurant that served the BEST chicken mole' that I've ever had. I'd have to dig through old photo albums to find the name though. There were also some great places on Isla Mujeres + Cozumel.
Best to look for the smaller, family owned places vs. the spring-break watering holes (Senor Frog).
Have a great trip!