The problem with Just Cause 2 is that the generated map doesn't allow for in-depth exploring. Far Cry 3 is a great game, it had a really good story that fit the theme, but it has a small sound bank, non-existent AI (like GTA V), and since the map is also generated, there's lots of floating trees and rocks, there's even a hole in a cave that lets you get out of the map (it's crazy). GTA V has nothing "under the hood" that makes it polished, nearly every mechanic is broken. Sure the outside map looks nice, but that's all there is to it. There's no interiors, and nothing that lets you interact with the game world.
I guess all three work differently, Just Cause 2 is about massive landscapes to mess around in, Far Cry 3 is about being trapped in a condensed jungle and finding the secrets it has, and GTA V is about living in a modern lifestyle. All three are different open-world games, whatever one you like the most is up to you.