I wouldn't have minded learning more about Maul back in 1999, but that was never his purpose. The real meat in the Sith apprentice sandwich was intended for Dooku, Sidious and Vader. Besides, as reference materials published over the years have said: Maul was but a placeholder to keep the seat warm until Sidious had his ultimate apprentice in hand, the one he would use to gain control over the galaxy.
Maul was just never meant to be much more than he was, and the recent Clone Wars
resurrection of the character has just been a bonus for fans of the guy who got tired of having little background information about him.