Isn't all entertainment just about Dopamine release (catchall for all other known and unknown 'pleasure' neurotransmitters. Zynga's games were decent enough at first. The problem is that for a business that is in the business of purveying entertainment, to be successful, it has to figure out a way of continually squirting out Dopamine in a subject without harming them (harming is more from business point of view than moral). Zynga's current game plays simply can't achieve that. Now if they can get the gambling license...
(it is approaching midnight, so please pardon my incoherence)
