For the natives of the Americas, there were very important things both good and bad that came to them in the Columbian Exchange.  On the good side, there were horses.  Horses changed the lives of groups of Native Americans such as the Plains Indians.  On the incredibly damaging side, there were infectious diseases.  These might be the most consequential things that went either way given that they devastated that Native American population.

The people from the Old World essentially got the good side of the bargain.  Most of the things that went from the New World to the Old were new kinds of foods.  Most importantly, the Columbian Exchange brought corn (maize), tomatoes, and potatoes to the Old World.