Story and voice acting.

To be honest, I expected a much more interesting storyline. In reality, it's just meaningless slaughter. The campaign is incredibly boring. I only liked the first chapter of the Sanctuary. And even there, only the first half was engaging; the second half was just blah-blah.

And, of course, a separate "thank you" for the voice acting of the characters. The city windows look like masterpieces against that backdrop.