I think especially for the money it's a decent food. Are there better foods? Yes. Kirkland food contains beet pulp which I don't like to see in foods, but it's definitely leaps and bounds better than Purina, Pedigree, Iams, Eukanuba, etc. For people on a budget, it's definitely a food I recommend, however I also let people know if they can afford it there are better foods out there as well so it just depends on the situation.
I had both of my dogs on it for awhile before I switched them over to Canidae, and they both did great on it, not a problem. I would say if your dogs do well on it then there is no reason to switch. Like Boxermommie said, there are better foods out there, but the kirkland brand dog food is really cheap for a decent quality food!
I use Kirland occasionaly. I mostly feed Solid Gold but swap back and forth. The dogs like it and have done better on it than alot of higher priced foods that I have tried. Their coats where great on the Lamb and Rice!