Just started the campaign here, and while dutifully impressed by the graphics, art direction, mo-cap, etc, one thing is sticking in my craw:
Cortana's voice direction is so bizarrely haphazard.
She just sounds all over the top in tone and inflection, and emotion, during in-battle chatter. Then gets all serious and reflective during cut scenes relating to her... situation.
It's actually distracting from the story scenario, the way she's all gung ho during play. They just crashed on an unknown world, are fighting scary new enemies, don't know what's going on, are desperately trying to get rescued, etc.
Otherwise, still plugging away.