Apparently Games for Google+ launched last week in the USA, but isn't yet available world wide. I haven't got access to it yet, and my appeal to not get kicked out from Google+ is still pending, so I don't have first-hand experience of the Google games yet. But from what I read the games are mostly games that already run on Facebook, and I've been playing several Facebook games over the summer. So here are some thoughts on these social platform games, with examples.
My current favorite Facebook game is Kings Bounty: Legions by Nival. The original King's Bounty game from 1990 was the predecessor of the Heroes of Might and Magic series. In 2008 the brand was revived in a series of quite good single-player games, and now there is a Facebook version. What is remarkable is how close in quality the Facebook version is to the single-player games. If you go into full-screen mode, the only indication that you aren't playing a single-player game is the list of friends at the bottom of the screen. The hex-map turn-based combat is pretty much identical to that of the single-player games. There is no comparison with simple cow-clicking games, in fact the game is actually quite hard. Even just following the main quest line is fraught with danger, as you risk the level of your enemies rising faster than yours if you don't do various side quests and farm lower level battles.
The main issue with Kings Bounty: Legions is that there isn't really a good reason why that game should be on a social platform like Facebook in the first place. There are token social functions like sending gifts to your friends, but the game is clearly designed as a single-player experience with very little social interaction. You can PvP your friends, but only if both of you are online at the same time, unlike many other Facebook strategy games which allow asynchronous combat.
Another game I've been playing a lot on Facebook lately is Zynga's Empires & Allies. This is more classic Facebook game design, think Farmville meets strategy games. The social interaction between you and your Facebook friends is a lot stronger, in fact you don't advance much if you don't have at least half a dozen friends also playing, because all troop updates are based on exchanged gifts. If you don't get gifts from your friends, you would need to buy these for cash, and they aren't even cheap. But even if this is unmistakably a Zynga game, the evolution from earlier games is clearly visible as well. There is a combat system based on a rock-paper-scissors balance. You don't just click stuff to make your city grow, you level up, build new troops, upgrade them, and lead them to battle. There is a big PvE campaign and asynchronous PvP battles against your friends.
Recently I started a new Facebook game called Master Dealer, which is another example of the evolution of Facebook games. This one isn't from Zynga, but it is an evolution of Zynga's popular Mafia Wars. Instead of having a primitive progress bar where you advance just by clicking on a button, Master Dealer has a "trading card" turn-based combat system. In a somewhat weird variation of social gaming, Master Dealer is a PvE game, but puts the profile photos and names of your Facebook friends on the computer-controlled enemies. Even if these friends don't actually play Master Dealer themselves (and are thus totally unaware that you just crushed them in combat).
If I ever get to play Games for Google+, it will be interesting to see how they handle social gaming, and if it will evolve in a different direction than Facebook games. In Facebook all friendships are mutual, if I am your friend, you are also mine. That isn't the case in Google+, I can be in your circles without you being in mine, and different circles can indicate different levels of interaction.
I do think that while games on social platforms still have some obvious flaws, one shouldn't totally dismiss them without a closer look. I believe that some aspects of them would be well worth implementing into MMORPGs. For example I'd love to see guilds being able to cooperate in an asynchronous manner, with everybody contributing at his own pace and timing, for example by building a guild castle together over months. The current cooperative mode of MMORPGs, where people need to be there at the same time, for the same block of hours, and preferably at the same level of skill and gear, is far too limited. Social platform games might not be quite that hardcore, but they do have some interesting approaches how to get people to interact without being online at the same time and intensity.