11. Halo ODST
It's easy to forget there's an open-world Halo out there; most likely because ODST arrived at a time when we were all bogged down with
serious franchise fatigue - not to mention you didn't play as Master Chief, instead an assortment of specced-up ODST drop-troopers (the guys that help you out across the trilogy's campaign). Okay fine, it's not exactly GTA, but in terms of having a large map to explore (New Mombasa, from Halo 2), ODST used it to pepper your objectives across substantial distances, tasking you to survive exploring the expanse whilst also tackling all sorts of patrolling Covenant enemies along the way. It completely changed the way you approached every scenario, ushering in the sort of mentality we now have with things like Far Cry, where each installation or outpost is met with a mix of stealth and "I think I can get in that way" trepidation. Touted now as Bungie's precursor to Destiny, with its more open-ended levels or various environments that see you exploring and taking on objectives when you see fit, ODST is a far more robust package thanks to a solid story and another stellar score from Halo composer Marty O'Donnell.