Cgi is only as good as the artisans, the time and budget. The Star Wars sequels have much better cgi due to a much higher budget and advances made since episode I by ILM. Lucas was self funding his movies and pushing forward technology that was not quite where he needed it to be for the prequels.The stuff they were trying to do was impossible like having photorealistic cgi characters like Jar Jar, or the other creatures and aliens in the picture. It all came off as kind of an animated movie. Lucas did call it his Disney movie, Phantom Menace.