The camera itself is still solid but the body is mostly made of plastic. It weighs significantly less than the G4 Bullet. The wall mounting bracket is slightly larger on the G5. The entire mounting hardware from either the G4 or G5 is compatible with the other however. There is no hookup for an IR Extender on the G5. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.