I don't mean the worst, I mean specifically the most annoying. Remember that guy Mud from Gothic, who would follow you around and say inane shit until you attacked him? Well, D:OS EE seems to be exactly like that in RPG form. Examples below:
1. Inane NPC voice overs that never stop, nor can be cancelled. These fucking epically moronic NPCs have nothing of value to say, they just say some long drawn out bullshit pseudo-theatrical line that is utter shite the very first time you hear it, but then they keep it on repeat loop. Makes me afraid to trade with NPCs, because those lines will just go on and on and on.
2. Equally bad combat voice overs/taunts. There is a fight in Black Cove, with a three-way between your party, the Orcs and the undead, and they keep insulting each other with the same stale bullshit lines, over and over, on repeat, and what's worse, the line doesn't even run in parallel to combat, the combat stops while they deliver the line. All 500 times.
3. Constant 3rd grade level humor in writing and quests that only a child would laugh at. There are legitimately funny RPGs that don't take themselves too seriously, like say Anachronox, but this ain't it. It's not funny, just retarded.
4. Main plot that is not just terrible on its own merits, but also tries to shoehorn the co-op angle, with 2 chosen ones instead of 1.
5. Endless procession of crates, containers and other trash to sift through. Yes, I realize this plagues most RPGs, but still.
6. Messy traps/combat side-effects. It's really easy to get wiped if you don't see some stupid trap under a bunch of crates, or during a fight your/their fire/lightning hits the wrong cloud/puddle.
The combat system itself is not bad, and the world design of at least the first area is good, but the quality of writing and this annoying bullshit sap the will to play this shitfest.