I myself would say G&G is somewhere either on the line of midlevel if not just a notch below. However this is a personal opinion made only from my own direct contact with the G&G line.
There have been cases of out of the box lemons but the same can be said about all other brands as well. The durability is fair, they will stand up to the normal use and abuse that a person would nornmally put an AEG through, however if you swing it around like a club Im sure you will wreck something.
Since not all G&G guns are created equal here is a link that will give some clarifacation.