Depends on what you mean by ‘good’ and ‘bad’. It’s better than food with grains in, but still worse than 100% real, human-quality meat. A cat’s liver enzymes are constantly looking for proteins to break down and turn into energy and blood glucose. If they don’t get enough meat protein in their diet, their bodies start breaking down muscles to try and meet their protein and amino acid needs.
Pay attention to the ingredients of your cat’s food if you’re considering going grain-free. Ingredient labels are quantitative, which means the ingredient with the highest amount is listed first. A cheap grain-free food could still have just as many fillers as an expensive food with grains. A better quality grain-free food will have the meat content listed as high up the list as possible (preferably the first and only ingredient) and have minimal fillers.
Make sure you pay attention to the type of protein too. Not all grain-free cat foods have quality meat. The packet might say grain-free or high-protein on the front, but if it’s made with “meat derivatives” (usually in powdered form), it’s still a far cry from the fresh 100% gently-cooked, nutrient-rich meat your cat really needs.