I certainly wouldn't call the ending of Middle-earth: Shadow of Mordor controversial like Mass Effect 3, I agree with you, it wasn't really -that- bad.
I guess I was just so disappointed with the ending because the game was really fun and I really enjoyed playing it, so I was expecting the ending to be just as exciting. To me, the ending felt very lacking.
The Nemesis system is very enjoyable at first, but over time it's not as "unique" as the developers claim... still, it is an interesting concept and it's well delivered. It certainly does add to the game's length and entertainment.