This is a great place to eat with real food, real flavor, and real Mexican atmosphere.
The restaurant is located in the middle of Mercado 28, the local market in Cancun. That may turn down a few fancy guys, but is better for the rest of us, as here you will find real people with great food.
El Cejas (the guy with eyebrowns) is the nickname of the owner, a Mexican guy with a great touch for seafood. Ask your taxi driver for the Mercado 28, and the rest will be simple enough. Enter the market through any door--it doesn't matter which one--and walk to the middle of the building. When you see lots of people happily munching on their fish or shrimp, raise your sight, and you will find a hand-painted sign "El Cejas". You will notice there are some other restaurants in the food court, but none as busy as this one. And the reason is the great food you will find here: from whole fried fish to ceviche (raw fish, shrimp, octopus, or mixed) to shrimps any style you want them.
The great thing is that the prices are down-to-earth, as this is not a tourist trap.
They also have another restaurant in Playa del Carmen between 24th and 26st Streets, between 25th and 30th Avenues.