Part of this week's discussion about D&D revisions, "Complexity and Option Fatigue," is over at Kobold Quarterly.
For the first half of D&D's life (back in the AD&D days), the game's complexity arose mainly from its open-endedness and its presentation. Players and DMs had to be skillful at navigating the game's labyrinth of rulebooks, which were laced with exclusive and often contradictory rules.
That shifted with the release of 3rd Edition. For the last fifteen years or so, most of D&D's complexity has come from what system analysts call option fatigue but is more commonly known as information overload.