> As andrewfelix said, none of the games Zynga makes has the same lasting potential as World of Warcraft or Call of Duty.
Financially, this needs to be adjusted for cost of production. I'll go out on a limb and say that a Call of Duty costs vastly more to produce than Words With Friends. It's entirely possible that launching 4 titles annually, where each drops off to 18 million users is a good business. In another genre, id Software was able to make a good business releasing essentially a single title every 2-4 years, targeted at a small subset of male computer nerds. So comparing e.g. WoW to Words with Friends may not be a valid direct comparison.
Without making a big judgement about Zynga one way or the other, I can say that the social/Facebook aspect is just about distribution of their games. That's just the channel, which also happens to be a good buzzword for pricing the IPO at the top of the range. Zynga's business is casual games, which has been a good business for quite some time. Remember all the pre-Facebook articules on how casual gaming is letting companies make money by including women in gaming? The Sims was often cited in this genre of coverage. But again, I'd put hard money down that The Sims cost vastly more to produce than Words With Friends.