I've been playing for about 3-4 hours now, playing through on Emily. I'm not sure how many different zones there are, but Karnaca seems MASSIVE. Plenty of little hidden nooks and crannies with story elements, loot and whatever else. Needless to say, it feels a lot more open than D1. Enemies are more intelligent than the first game it appears. They're more aware and can spot you fairly well. I can't really comment on the story as I haven't played through much of it, but man do the clockwork soldiers seem fucking cool. I can't really give a solid judgement because of played so little, but I can honestly say if you enjoyed D1 you'll probably love this as well.