Online chicken noodle soup recipes contain mostly the same things - chicken, noodles, stock, vegetables - and for the most part taste the same.  However, they taste completely different from the soup in many restaurants (such as Old Country Buffet or my favorite, Perkins').  I can't figure out how to make my soup taste like that.  It seems like the main difference is how thick the soup is... but simply adding less water doesn't do the trick.  How do restaurants make their broth so thick? (should I be making my own broth?) 
None of the answers so far mention collagen -- specifically, using a stock made from roasted and cracked poultry bones.  You don't have to roast the bones, but you do need to crack them -- use a large, heavy knife or cleaver (not a chinese vegetable cleaver, you'll screw up the edge) to chop the bones up into about 2" to 3" pieces (5 to 7cm).  Put them in cold water, and slowly bring it up to a simmer, and just leave it simmering for a few hours.  You can add vegetables, too, but you'll want to pitch them, as they'll have been overcooked by the time the simmering's done.  Then strain everything, and use that as the base of your soup.  If your refrigerate stock that has enough collagen in it, it'll set up like jello, and hold its own shape.  Starches can work, but they're not ideal for soup -- flour (unless cooked as a roux) leaves a raw flour taste and cloudy soup; tapioca leaves little granules in there; corn starch will break down if you cook it too long. 