The G8 used to be criticized as an evil capitalist group of powerful countries that determines world politics and economics without legitimacy like the UN. There has not been much of such criticism at this year's summit in Japan.
This time, lack of effectiveness was the most common criticism. The G8 is increasingly seen as a Western talking shop that is doing photo-ops with rock stars and third world leaders, but fails to act on its past promises on development aid and is increasingly incapable to shape international economic affairs.
Besides, Senators McCain and Obama recently had a dispute as to whether Russia should be excluded from the Group of Eight.
Consequently, there have been several reform proposals to make the G8 more effective:
L20: upgrade the existing G20
G13: G8 + the "outreach 5"
G9: leading market democracies
G3: US, EU & China
G3: US, EU & Japan
The Atlantic Community explains these proposals and asks: "Should the G8 be enlarged to include new major international players or contracted to ensure effectiveness?" If you register on Atlantic Community, then you can vote on the above options.