Social Gaming is slightly different from arcade gaming, and the heavy duty PSP3, XBox, Wii world of gaming. Some observations on my research ( ;) ) on social gaming across internet is as follows-
There are mostly 3 types of social games-
1) Quest- Build a town/area/farm to earn in game money or points
2) Fight- fight other people /players /pigs earn in game money or points
3) Puzzle- Stack up, make three of a kind, etc
Most successful social games are a crossover between the above three kinds of social games (so build and fight, or fight and puzzle etc)
In addition most social games have some in game incentives that are peculiar to social networks only. In game incentives are mostly in game cash to build, energy to fight others, or shortcuts in puzzle games. These social gaming incentives are-
1) Some incentive to log in daily/regularly/visit game site more often
2) Some incentive to invite other players on the social network
A characteristic of this domain is blatant me-too, copying and ripping creative ideas (but not the creative itself) from other social games. In general the successful game which is the early leader gets most of the players but other game studios can and do build up substantial long tail network of players by copying games. Thus there are a huge variety of games.
However there are massive hits like Farmville and Angry Birds, that prove that a single social game well executed can be very valuable and profitable to both itself as well as the primary social network hosting it.
Accordingly the leading game studios are Zynga, Electronic Arts and (yes) Microsoft while Google has been mostly a investor in these.
A good website for studying data about social games is http://www.appdata.com/ while a sister website for studying developments is http://www.insidesocialgames.com/
As you can see below Appdata is a formidable data gatherer here (though I find the top App – Static HTML as both puzzling and a sign of un corrected automated data gathering),
but I expect more competition in this very lucrative segment.