Anyone who says all the food on the ship is "inedible" is either grossly exaggerating or the world's pickiest eater.
Overall, think the food is good. I would consider several of the items in the MDR (short ribs, brisket, soups, bitter and blanc, etc) to be great.
I would never let one or two anonymous opinions on a public website (especially negative ones, complainers like to complain) set my expectations. Tens of thousands of passengers board Carnival ships every week as repeat guests. If the food was truly that bad, why would so many people choose to sail with them again?