The Future was an alternate world where Aku had conquered the whole planet after he sent Jack through a time portal. It was also the main setting location, plot throughout the whole adventure of the series.
When Aku teleports Jack with his time portal and sends him into the future, many changes can be seen, the difference between the past and the future is that the future possess way more enhanced or improved buildings, lots of robots, flying machines, strange animals that are modified and turned into cyborgs, that many of them are saved from the great warrior Jack.
But that's not all, the future has its bright side too, except the large industrial buildings that take place all over the world, some earth structures are still not ruined and yet have their fascinating beauty which seem never to be destroyed from the evil forces.
After 50 years, Samurai Jack still remained and cannot be aged physically due to the side effect of Aku's Time Travelling spell. He still vows to finding a portal to get back home to the past.
This dystopian future was unmade after Jack successfully destroyed Aku in the past. Since there was no Aku to spread his evil influence, it is possible that it has become more pleasant than before. However, the existence of every single being in the future might be affected since Aku, in some ways, was the catalyst for their own existence, and all events that have occurred will be undone as well, thus altering reality.