Much has been said about the upcoming expansion for Diablo 3, which is Reaper of Souls. Changes are coming to the game, making for a better overall gaming experience that will put it a few more steps forward in the action RPG genre that its grandfather had innovated. However, there is so much more coming other than what had already been talked about. Aside from just the new character class, removal of the Auction House, the new Paragon 2.0 system, and so on, there are more additions that will make this game feel very different from its original form that was released back in May 2012.
The major change in the game includes distinction between Campaign Mode and Adventure Mode. The first one is the game mode that everyone knows, which is following the story of the Nephalem, the heroes of Sanctuary that have taken upon the quest to cleanse the land of evil. It's basically Diablo 3 as you know it, so you should be able to understand what it is all about. As for Adventure Mode, it is a new way to enjoy Diablo 3 by having all waypoints unlocked, which lets players roam free and take on challenge at their own whim. These two modes can be accessed at anytime without much restriction, so players can have a greater degree of freedom with their gameplay.
Adventure Mode is for those who want to build up multiple characters, but don't want to have to play through the singleplayer campaign multiple times over. Instead, you are now able to farm for experience and Diablo 3 items in a specific location at the desired difficulty repeatedly as desired without having to reset the quest and so on. You no longer have to travel great distances and spend most of your time rifling through the lesser parts of the game to achieve your objective. This mode also includes two features called Bounties and Nephalem Rifts, which are designed to mix things up in this gameplay mode.
Bounties are optional objectives that come up at random, wherein you can accomplish them in order to stay engaged in Adventure Mode. They present new content in the game and let you earn experience and loot in a directed manner, so farming and grinding doesn't get too monotonous. Bounty Hunters will then earn a new item called Rift Keystones, which grants access to Nephalem Rifts. Previously called Loot Runs, they are basically random dungeons that players can run through for 10-15 minutes for tons of loot and experience. These dungeons are a surefire way to reach areas with good concentrations of monsters, which is good for farming runs.
In order to access Nephalem Rifts, just bring a Rift Keystone to a town and get to the Nephalem Obelisk. You can then go through the portal and start running through the dungeon. You get Rift Keystones mostly by completing Bounties, but you can also pick up some at random in the Adventure Mode. Once you are able to familiarize yourself with these two modes once Reaper of Souls come out, you should be able to have much more fun in Diablo 3.