Putting aside the United States, which ranks third, the four most populous countries are China, India, Indonesia and Brazil, accounting for more than 40 percent of the world's people. And all four have made great strides. Indonesia had solid economic growth during the entire decade, mostly in the 5 to 6 percent annual range. That came after its very turbulent 1990s, marked by a disastrous financial crisis and plummeting standards of living.
Even in the United States, the fact that people are living healthier longer represents an improvement above and beyond the GDP statistics.
Earlier, Bryan Caplan pointed out that we did not have a world war, Hitler, or the Soviet Union, which is an improvement the decades from 1911-1990.
Combine economic and geopolitical developments. If you take a random sample of people from around the world in various decades, chances are your sample in the aughts will be the healthiest and happiest.