Had a thirty minute play sessions with a developer next to me. I told him frankly that I really don't like LOTR but that I'm very interested in the Nemesis system, which made him smile and go "okay, cool." As I was futzing around, he was explaining things, the systems, the wild life, and it was great. We tried to make plans to go after certain orcs, but every time something weird would happen and they would die by some animal or funny coincidence. We laughed a lot during the demo and it was just plain fun.
The open world only makes sense because of the Nemesis system though: you create your own targets and missions by selecting your approach to taking over that region. You go after orcs with a certain purpose in mind and you set out to do it, and things will happen along the way or at the location of your next target. There's Batman-esque combat, the possibility to be stealthy-climby like Assassin's Creed, there's other stuff too - but it's all connected through the Nemesis system. And as far as I can see, it really works as advertised. Orcs remember your actions, and your actions influence the inner workings of the orc hierarchy. Don't think you can play the bits around the Nemesis system or something, there's no such thing.
Also, wild life is more dangerous than any orc. I could handle ten orcs while trying to keep the converstation going with the developer sitting next to me. But it only took one wolf/mountain cat-ish creature to chomp at my throat and me missing the prompt to kill me :')