"Social games" are the least social variety of game that has existed over the past 5,000 years. They're even less social than typical video games. With console games like Final Fantasy 6 there was, at least, the process of going to school and talking about the game with other kids. There was a social "meta" game. Magic had a similar metagame that was deeply social: you had to engage with other people to figure out what strategies people were coming up with and what the new deck types were. Zynga games don't have that because almost no adult would ever admit to wasting 5 hours per day on Farmville, because it's just too damn embarrassing.
These "social games" exist to generate addiction without content. As peoples' immunities build, that's going to become increasingly fruitless from an economic perspective. And the only thing "social" about them is that they market themselves through social networks. Zynga is, in essence, Facebook's tapeworm. It's also, in my opinion, responsible for a large fraction of the "social network" fatigue that's setting in now.
There was a (failed, alas) proposal at Google to focus on high-quality games for Google+. It was called the Real Games (or Excellence in Gaming) initiative. The idea was that we'd support independent designers who'd give us quality games, instead of publishing the dreck thrown at us by mainstream publishers. We'd have the developer code up the game logic and UI, and we'd take care of web-scale, player matching, and analytics. (We'd also be able to provide a platform for playtesting, which is a major limiting factor for amateur game designers.) I wanted to focus on German-style board games, the best social games (e.g. Apples to Apples), 2D "retro" RPGs, and the most innovative casual games... but inevitably we'd cover the whole space.
The business logic was as follows. Every social network needs to start off seeming upscale, but "upscale" on the Internet has more to do with content quality, intelligence, and in games, NFC (need for cognition) than economic status. Facebook had a huge high ground because it started in the Ivy League. Google+ needed something similar. Providing an extremely high-quality platform for excellent games that can't be found anywhere else would give us this.
We could also integrate these games with Hangouts and make the experience genuinely social. I'm obviously biased, but I think this was one of Google+'s biggest missed opportunities of 2011.
Also, in mid-2011, Facebook's brand was damaged (more than it is now) by these games, due to the game spam problem. Facebook had actually fixed that by then, but reputation is always a lagging indicator and we had a great opportunity to use this to brand ourselves in the wake of the first signs of social network fatigue: "We Won't Waste Your Time With Shitty Games".
You've probably never heard of Google+ Games. That's a good thing. The higher-ups ignored Real Games and took a "Me, too" strategy that failed.
Taking a broader perspective, I've thought a lot about the social space and about games, and I think the fundamental way in which these networking products are undeserving people is that there's no focus on improvement. The space seems to be all about documenting what is (and selling the data to advertisers) but very few (Meetup is an admirable exception) are actually trying to improve the social theater and expand the network. The next great social network and the next great game platform will be ones that improves human interaction in creative ways that few people had ever thought of.