A good rule of thumb is to check the ingredients. If a food is chicken flavor, the first ingredient should be "chicken", not chicken by-product or chicken meal. If you are concerned about weight, try adding in some canned diet. Can food is more similar to what cats would naturally eat. Also consider portion control. For a standard size cat, a level 1/4 cup of dry food morning and night should be sufficient (or one 3 oz can morning and night, or 1/2 of a 5 oz can morning and night with a level 1/4 cup of dry for the day).
Dry food is generally higher in carbohydrates. Just like a cake needs flour to hold it together, dry foods need flour or corn or something similar. This is unnatural for a cat. Compare it to our high carb foods - chips, pretzels, cookies - we can eat them all day and never feel full. A housecat will eat out of boredom just like we do, and may not feel satisfied on dry food, and end up overeating. By the way, regular dry food is not better for their teeth. The only dry food that can actually make a difference when it comes to tartar and plaque are diets that are specially designed to do so (t/d, oral care, dental health, etc.)
Canned food is higher in protein and generally has fewer carbs. If you think about what cats would eat in the wild (mice, birds, lizards - mostly muscle/protein and fat) it is a more natural diet for them. The higher protein will leave them feeling more satisfied, just like when we eat high protein foods. Think of steak and eggs - you can only eat so much before you feel full and can't take another bite. Also canned food has more water content, which is good b/c cats originate from desert creatures and typically don't drink enough water.
Dry "diet" and "light" foods tend to be high in fiber - the bulk may make them feel fuller, but it may need be meeting their nutritional needs.
In general, finding a good food is a challenge. No one company knows everything there is to know about cat nutrition. How ridiculous would it be for someone to hand you a bag of crackers and say "Thse are fortifed with everything you'll ever need. Eat this and only this for the rest of your life." You would look at them a little funny, wouldn't you?
Now if you are looking for unprocessed, organic way-of-life type foods that's a little more difficult. That's even fairly difficult and inconvenient when humans try to do it; unfortunately that's just the world we live in. But for the most part, any higher quality food you can find at reputable pet supply stores should meet your cat's nutritional needs.
Keep in mind, too, there is "ideal" and there is "reality." Reality is that not every pet owner can afford state of the art medical care, or the most expensive organic food, or has time to prepare specialty raw diets (I am not an advocate of raw diets, btw). If all you can afford is Iams and Fancy Feast, well so be it. It's like people eating Doritos, Wendy's or ice cream. Sure it's not the best thing ever in the long run, but it won't kill you. I'd just try not to buy the cheapest thing in the grocery store, as those tend to have lots of fillers and little nutritional value.
As if that's not long winded enough, in any discussion about cat nutrition I need to add that cats are obligate carnivores. They MUST eat meat. Vegitarian diets will NOT meet their nutritional needs. I've never met a vet who disagreed with this.
Good luck finding foods for your little guy.