I'm finding the combat to be pretty much identical to the other two games. I'm starting to do worse right now because I've been playing all day and my thumbs are getting tired, but all in all I'm not having too hard a time.
I'm not quite invested in the story yet. I've put in about 5 or 6 hours of gameplay, and I can tell that I'm not even close to being done. Hell, I've only run into two of the 8 assassins so far!
I'm really liking that the entire map from Arkham City is present in this game, in addition to a whole other area of Gotham that's roughly the same size. It certainly makes sense to do it that way; it's not like that area of Gotham would randomly not be around. I'm wondering what villains I'm going to run into that I haven't already.