The downside to the Facebook Gaming genre, is the dynamics of the social environment. When Mafia Wars grabbed hold of Facebook like a raging wild fire, The invite system was abused, Also creating a hostile reaction from ex players and patrons, constantly annoyed with the relentless invites, forcing the team at Facebook to re-design how the "invite friend" function works. Thus changing the social dynamics, decreasing people who you can come in contact with.
With Zynga falling through the proverbial legal cracks in the system, with their copy right infringements, and shenanigans, suing the Brazilian company, they still continue to hold on by the skin of their teeth. And Yet despite all the negative publicity, so many ignorant players continue to use their product. Destroying the integrity of Social Network Games.
With companies like Microsoft, and Siri discontinuing certain app stores on cell phones, allowing less access to certain games, or misleading ads trapping buyers into something they regret purchasing, sales will drop dramatically over the next few years.
I can rattle on and on about the good and bad of gaming with each one of the individual platforms. But Ill make it simple and sweet...
PC and Console gaming will never die out for the simple reason, there are devout crowds in each genre, that will not permit it. The demand is still great enough to produce games for each.
Even better news to consider is with the new technology that is out there today, like Cryengine 3, game companies can create cross platform and cross OS gaming products. Gaming will never die! Not for any type, on the basis of demand, and technological evolution.