1. Sliding down tiny slopes. I could literally just step over it, but instead I'll slide and slide. And when I finally do manage to jump up that slope...
2. Random invisible walls. Not at the edges of the map, which is understandable, but all over the map. Ridges, tree lines, foliage. In fact everywhere except the ledges that followers like to shove you off.
3. The big green button (on Xbox One). The artists did a great job at creating atmosphere and mood. All of which is ruined when the big green button and 'Interact' floating text draws your attention away from it. For example, at the end of Haven, when you're struggling through a dark, forested mountain pass, in a blizzard at night. Very atmospheric, until you see the big green button hovering over the campfire. A less intrusive crosshair would be better.
4. You'd think if you're making a party based game, you'd figure out a way to stop the party members bouncing around like toddlers on a sugar rush every time you stop walking for a moment. When I'm having very serious conversations with kings and demons, the mood is invariably ruined by Cassandra leaping around like a clown on a table/bush/NPC's head in the background. Once I was even pushed out of a conversation with an NPC when she charged me from behind.
5. The opening screen. Mages and Templars walking with slow dignity to their doom at the Conclave. Wait! Now they're scurrying along like a Benny Hill sketch! And now it's all slow and dignified again. Always makes me chuckle.
6. Loading screens full of interesting text suddenly disappearing. Hey, I was reading that!