The ground is 100% effective against all known combat aircraft
Their rating system is based on four color-coded levels in three areas, profanity, sex and violence. They've gathered extensive documentation of "instances of profanity, sex, violence, and substance abuse" and compiled it into objective ratings.
The first five games on their list include clickable links with more specific information and descriptions. You might be able to judge from those, what to expect from the other five games listed.
Family Media Guide writes that its system produces ratings "superior to the existing ESRB... review approach." The superiority may depend on how parents and others wish to use the ratings, how precise they want to be, what sort of games they want to avoid, etc.
We encourage any parents out there to be their own judge, of course. Keep your ooko to the ground and your shlem on your gulliver. That's it for this raskazz. µ