The 20th century saw more scientific advancements than any prior century. When Star Trek was first televised, everyone thought the communicators were cool. They only talked to the ship. We have cell phones that can reach almost anywhere in the world.
It was the worst century because it included so many wars, including WW1, WWII, Korea, Viewnam, Iraq and all the other places where people have died for senseless reasons.
It was also the worst century because class division began to developed--the haves, and the have nots. We can hope that in the 21st century, we can continue our scientific advancements, put an end to war and work to help the less fortunate enjoy the good life that too many of us take for granted.