The open world is sizeable and you can climb on the rooftops and stuff, but it is a touch concerning that the PC Gamer hands-on said that they were playing the opening 30 minutes of the game and it wasn't clear to them why the game was open world. This is important because MindsEye just released and it had the exact same problem. Supposed there's sidequests and random NPC encounters and open world crime systems and stuff, but we'll see.