George Lucas has said "I cannot make a movie according to what ,y fans want". He is exactly right. Episode 1 was a good movie in that it served it's purpose(I enjoyed it, and have the DVD), which was to introduce the character, Anakin Skywalker. You have to remember what Star Wars is about. It is basically, the story of a family. The Skywalkers.
Darth Maul served a purpose. When his character's purpose was done, he was eliminated from the story. that is what moviemaking is, keeping integral characters and eliminating irrelevant characters. That is storytelling.