The story. I notice story are going down after Halo 3 due to much focus on multiplayer. I honestly think there should be two teams, one campaign and one story both have their own art designer and the jobs. If 343 already is thatway then I have more faith in CEA ( not saying I didn't just more).
Randomness. Halois the most random game I played. On Halo 2 on Cairo Station I fired my SMG when suddenly crossed a loading zone and I couldn't make it stop. Remember in H2 when you continuosly fire SMG your aim goes up ? I was walking around station looking up at ceiling while firing my gun till 3 Elites found me ...