Purina is actually a 1 star dog food - not very good.
Here's a review
Dog Food Reviews - All Products - Powered by ReviewPost
The first ingredient listed is corn and is difficult for a dog to digest. Many other bad things about it. I think it's been recalled quite a few times.
Some good foods -- Merrick, Wellness, Innova. There's a list on this forum stickied somewhere of the best dog foods and you can e-mail and ask for samples.