If you don't like to see locals eating while sometimes smoking, if you don't like tiny tables, if you don't like cut papers instead of napkins, don't go there.
But if you do like fresh fish and seafood grilled to your taste, simplicity and good prices, local ambiance, definitely this is your place!
Fascinating seafood on ice, simple tastes, basically you can choose between grilled fish/seafood or a fritto misto - a mixed fried fish platter with shrimps and cuttlefish. All come with saffron rice, marinated olives and two types of local harissa-like sauce.
And all at a very-very competitive price! I had a grilled spiny lobster and a cuttlefish with a big bottle of mineral water and paid MAD 116, which means about 10 euros!
Is it a fair price?

Best restaurant we visited in Marrakech by a country mile. Fantastic seafood and brilliant prices. Didn't rate the Lonely Planet guide on the whole but this recommendation was spot on. We had a kilo of langoustines, a kilo of calamari and half a kilo of sole for about MAD 380 (GBP 28 approx). Fish was super-fresh and superbly cooked.