Look up your Iams formula here: http://www.dogfoodadvisor.com
You'll find a breakdown of the ingredients along with an explanation about why the food may or may not be great. Some Iams formulas rank as low as 2 stars, while others rank as high as 4 and are probably ok. Personally, I won't buy any of their formulas because they put more money into shoving their food down everyone's throats than they put into producing a quality product and letting it speak for itself.
They also do some kind of testing on animals that is unnecessarily cruel. Or something like that. . .I haven't looked into it too much because I also think it's overpriced so I'm not going to buy it anyway. But if you Google it you should be able to find something.
The original formulas are fairly crummy, ingredients-wise. The Naturals line doesn't seem too bad.
Maybe its just me, but I don't trust and would never feed my dogs any kind of dog food that is advertised on TV, sold in a grocery store/supermarket or recommended by a vet - Just me though I wont share my thoughts and opinions as to why, because maybe someone would get offended or disagree, but like everyone else has already mentioned.. Iams is a poor quality food, there is much better for similar price. Maybe if they put more money into the care and quality of the food rather than dumping it all into advertising and marketing, etc it would be better? Who knows.