In my opinion Science Diet is not a good food.
These are the ingredients of Science Diet Original. Chicken By-Products are not good, and corn is bad for dogs. Here is a good link to explain the rest of the ingredients.
http://www.sniksnak.com/ac/petfooddefinitions.html
Ingredients
Chicken, Ground Whole Grain Corn, Ground Whole Grain Sorghum, Ground Whole Grain Wheat, Chicken By-Product Meal, Soybean Meal, Animal Fat (preserved with mixed tocopherols and citric acid), Corn Gluten Meal, Brewers Rice, Chicken Liver Flavor, Soybean Oil, Dried Egg Product, Flaxseed, Potassium Chloride, Iodized Salt, Choline Chloride, Calcium Carbonate, vitamins (L-Ascorbyl-2-Polyphosphate (source of vitamin C), Vitamin E Supplement, Niacin, Thiamine Mononitrate, Vitamin A Supplement, Calcium Pantothenate, Biotin, Vitamin B12 Supplement, Pyridoxine Hydrochloride, Riboflavin, Folic Acid, Vitamin D3 Supplement), Vitamin E Supplement, minerals (Ferrous Sulfate, Zinc Oxide, Copper Sulfate, Manganous Oxide, Calcium Iodate, Sodium Selenite), DL-Methionine, preserved with Mixed Tocopherols and Citric Acid, Beta-Carotene, Rosemary Extract.
Here are the ingredients of Natural Balance Ultra Premium, which is what I feed Loki. It's on the acceptable list by the Whole-Dog-Journal and while they are better foods out there, he has a sensitive stomach and this works well for him.
Chicken, Brown Rice, Duck, Lamb Meal, Oatmeal, Pearled Barley, Potatoes, Chicken Fat (preserved with mixed tocopherols - source of Vitamin E, Citric Acid, and Rosemary Extract), Natural Flavor, Tomato Pomace, Canola Oil, Brewers Yeast, Lecithin, Choline Chloride, Carrots, Potassium Chloride, Whole Ground Flaxseed, Dried Kelp, Sodium Chloride, Parsley Flakes, Calcium Carbonate, Zinc Proteinate, Ferrous Sulfate, Zinc Sulfate, Vitamin E Supplement, Vitamin B-12 Supplements, Ascorbic Acid (vitamin C), Taurine, Yucca Schidigera Extract, L-Lysine, Manganese Sulfate, Niacin, Riboflavin Supplement (Vitamin B-2), Copper Proteinate, Copper Sulfate, d-Calcium Pantothenate, Vitamin A Acetate, Inositol, Folic Acid (Vitamin B, Pyridoxine Hydrochloride (Vitamin B-6), Thiamin Mononitrate (Vitamin B-1), D-Activated Animal Sterol (source of Vitamin D-3), Biotin, Ethylene Diamine Dihydriodide (source of Iodine), Cobalt Sulfate, Vitamin K Supplement, Sodium Selenite
So, the truth really is in the ingredients, not necessarily the label. THey all claim to be wholesome and "natural" and good for your pet.