I was totally and completely addicted to WoW for two years. Almost lost my girlfriend, friends, etc. When I finally quit I had the shakes. Literally. One thing though is I've never saved more money than when I was playing WoW because I never went out. These newer games do seem to have a different financial model that exploits addiction in potentially a much more dangerous fashion.
It's mostly that they're "casual" and, most importantly, primarily mobile. Which means they follow you everywhere as you conduct your life.