Chess site addiction

Okay, I've been here at Chess.com for twenty days now and remarkably I'm nearly always here when I'm at my computer. What elements of this site explain its appeal?  I've been playing turn-based chess for four years, so the nature of the site is nothing new. Other sites where I play have tournaments, teams, and better database features--all central to online chess play,--yet, this site seems to captivate my interest.