Iams isn't too bad a food, it is just expensive for what it is. It uses beet pulp as a filler and its meat content is not that great and, iirc, it uses meat derivitives (bits and pieces
) For the money you pay you can get better foods e.g skinners, csj or arden grange. Also, iirc, there are some ethical arguments against the producer P&G.
I've used it/eukanuba for mine and they thrived on it and wolfed it down, however I've since changed to Arden Grange for the above reasons.
If your dog isn't keen on it then, tbh, there is no reason to keep it on it, just remember and do the change gradually.