I really like the open world.
Some of my favorites are Skyrim (you can go Anywhere! See a tower in the distance? Well figure out how to get there.) and Shadow of Mordor (you could just see so far!)
Halo:Reach (not open world, but had parts that were like it.) Many games have 'background' villains, and you can walk up to a line where they can't bother you. Not so in Reach, you get close to anything, and will start bashing you. Make the game feel more real.