Twinfinite reports that Shadow of War's Nemesis system will be better in comparison to Shadow of Mordor:

5 Big Improvements Coming to Shadow of War’s Nemesis System

More Variation, More Choices

Middle-Earth: Shadow of Mordor’s Nemesis system was easily the most unique aspect about the game, making it something truly memorable that even garnered multiple Game of the Year Awards. Well Monolith isn’t content with what they had in the first title, as they’ve drastically improved the Nemesis system, adding in more variation and choices than ever before. At E3 2017 we got an extensive hands-on session with the game, where we got to see a few of the new changes in action.

The basics of the system are intact, requiring you to damage enemy chieftains and leaders before you’re able to dominate them. Bringing up the main menu displays a whole hierarchy of enemy forces, leading all the way up to the army’s leader. During my time with Shadow of War I decided to first take down an enemy Warchief, warping him to my side in order to boost my forces and weaken the enemies’ before taking the Fortress Siege head on. Of course, much like the first game, in order to make the Warchief appear I needed to meet a few requirements.

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Thanks Farflame!