The short answer is that using Google+ and the web for internet gaming sucks. But simultaneously it doesn't suck. How can that be so?
Understand that since 2007 or so I been using Fantasy Grounds plus Skype on a near weekly basis. So far I gamed using D&D 4e, Castles & Crusades, GURPS, and Swords & Wizardry. Fantasy Grounds is in my opinion the Cadillac of Virtual Tabletops. Google+, and the use of various web tools like Twiddla is far inferior to using Fantasy Grounds in every respect except one.
Google+ and most of the web tools just work. And they easily setup by the average gamer. Fantasy Grounds and similar software require both an outlay of money and the knowledge of how to open a port. There are server based tabletops (web and non-web based) but they currently cost $$$, and not as feature rich as fantasy grounds. While most of these are only small barriers they are a substantial barrier to just getting a game together and having a session.
In the hands of a group of gamers Google+, Twiddla and other webtools are "good enough" and the have the virtue of allowing anybody with a internet connection to quickly get on a game. There is a element of trust without a online dice rollar so some maturity is needed among the gamers in order to make this work.
The missing elements that I think is needed for Google+ and Twiddla is a dice roller for Google+ and layers with locking for Twiddla. Twiddla also need mouse rotation for object.
After using Google+ I am glad to have a viable alternative to Skype.
The Google+ client on iPad sucks for not having access to the chat while in a hangout. I have to do this complicated dance of being on my computer and the iPad (because I don't have a webcam) to use the hangout full capabilities.
If you and your group are finding that you play tabletop on a regular basis you owe it to check out Fantasy Grounds if there is support for your favorite RPG rules. There are a lot of improvement over the Google+ plus Twiddla combination. I plan on later this year to upgrade to the Ultimate version so folks can use the free demo version to connect to any games I run.