Extremely addicting gameplay loop. The open world size felt perfect, big enough to have plenty of variety in scenery but small enough that you're always within a short run range of a mission or an event. I tend to barely use fast travel in open world games and Shadow of Mordor felt made for people like me.
Speaking of variety, there's very little of it when it comes to enemies. Captains and Warchiefs having their strengths and weaknesses is cool but their strengths outright invalidating some game mechanics can feel pretty lame.
The overall controls feel very iffy. It's that Assassin's Creed style climbing and running, for lack of a better term, that leads to a bunch of frustrating scenarios where Talion just refuses to climb to a rock that's 3 inches to the left of him after having just lept 10 feet to grab onto a ledge. Not to mention the myriad instances of getting 'stuck' against a corner or a small rock.
Story wise I didn't get a ton out of it either. I'm a casual LOTR fan(and casual is a load bearing word here, I've only seen the movies basically) and I felt like I was missing a ton of context throughout. It still did enough to keep me motivated to go from point A to point B and nothing felt outright bad, just that the target audience is probably people who are more involved in the LOTR universe rather than someone who last watched the films a decade ago.