Just one aspect: Crime rates are down because lead concentrations are down. Once unleaded gasoline became the law of the land and gasolines that used lead as an additive were banned, lead concentrations started decreasing in the atmosphere and the water supply. This had a huge impact on the crime rate. Even small amounts of lead can trigger psychotic rages, mental retardation (not necessarily just in terms of IQ, but emotional intelligence as well), and a variety of other health problems. But lead concentrations, it would seem, resulted in more violent crimes, and those rates have been steadily declining (despite any statements to the contrary) since the mid-1970s as tetraethyllead was phased out of gasoline. Now only Algeria, Yemen, and Iraq continue to use lead additives in their gasoline, compared to everyone in the early 1970s.
Do lower crime rates make the world a better place? Generally speaking, yes. If there's less violent crime, I am less likely to be murdered, and I consider that a good thing. Are there still problems? Of course. There always will be, and the world is not a perfect place. Is it better than it was say... fifty years ago? I can't speak as someone who was alive fifty years ago, but yes, generally speaking, I believe it is.