Now that you know that your son is okay eating rice cereal, you might want to add another puree for flavor, especially given that you say he was not a fan of the cereal when mixed with water. Maybe some carrots or very ripe banana (so that it is sweet)? Also, my son never ate the cereals or very many purees for that matter. He did not like the texture. Five months is pretty young still, so I wouldn't worry too much. You might want to hold off on the rice cereal for a week or so. If nothing has changed in a couple more months, there could be other things going on (none of which is terribly serious), but I really would not worry too much at this point. It doesn't sound like you are doing anything wrong; it just sounds like you have a baby :) You might want to buy "Child of Mine" by Ellyn (Ellen?) Satter. Many pediatricians and pediatric nutritionists recommend this book, and I found it to be a lifesaver. It is basically an instruction manual for how to feed your child so that he/she develops a healthy relationship with food. It is a truly wonderful book.
K.