Chinese characters/Japanese kanji are overly complex and full of nonsense. Their forms are limited by the fact that they were originally written with brush and ink. Modern writing instruments allow much more versatility–neat little circles, filling in, and much more detail.
As can be seen in the comparison below of ids and kanji, ids take a small fraction of the time to write. And ids represent things and ideas with more true-to-lifeness, making them easier to recognize. They are also embedded in families, with the same or related components for related ideas. For example, all ideas conveying “danger” and “safety” include the simple id for “cliff” because being near a cliff edge is my chosen metaphor for danger. An important class of id families is “graphic opposites,” in which ideas with opposite meanings are represented with graphically opposing elements–see good/bad, short/long, and the directions NSEW. Kanji ignore such relationships.
Another huge difference: ids, as I conceive and do them, are ever-creative, but according to a Japanese I spoke to, they don’t make their own or new kanji.