As nice as it is to see a different side of the story, some of us actually misses the rest of Middle Earth. Since Shadow of Mordor is set in Mordor, we only got to explore Mordor but not the other places in Middle Earth.
Fans are hoping that if Monolith does come out with a sequel for the game, we would be able to explore places other than Mordor. Although it might not make sense to travel out of Mordor since the title of the game itself suggest that Mordor should be our main focus, we would like to see the developers try to incorporate the other parts of Middle Earth into the game.
As of now, nobody really knows if there is going to be a sequel but many fans seem to believe that there is going to be based on the ending of the first game. Of course, the developers probably made the ending that way so that they can pick it up anytime they wanted to. That does not mean that they will pick it up.