The sequel to Shadow of Mordor is called Shadow of War. Warner Bros. hasn’t quite announced this yet, but Target spilled the news early (lol) along with the box art and some info (via NeoGAF).
From what I’ve heard, the story will be based on Talion and Celebrimbor (the two protagonists from Shadow of Mordor) working to forge a new ring that’s as powerful as Sauron’s. The Nemesis system is back, obviously, and there are new stronghold mechanics, new special abilities, and all that jazz.
More info to come whenever it’s officially announced. For now, let’s again laugh at Target.