Columbus opened up America for European colonization (if you speak a Indo-European language in the Western Hemisphere you are already in Columbus' debt), Christianity, and rule of law. His highly publicized journeys helped mold the world.
Places like South Dakota and Venezuela oppose celebrating Columbus' landfall, claiming to honor Indian opposition or culture this blames Columbus for things that happened well after his death. That is like blaming Jesus for the violence in Northern Ireland. The "real" reason for the change politics. The Venezuela change is due to Chavez trying to rally anti-western support for his power grab while South Dakota changed to "Native American Day" because Governor George Mickelson wanted Indian support for his reelection.
Other places celebrate today differently. Today is Discovery Day in the Bahamas, Hispanic Day in Spain, and Día de la Raza in many Latin American countries. Día de la Raza is named after the Spanish race and not the mestizos.
Columbus Navigation has excellent information on the man and his journeys. I have posted the maps below of the world changing travels.