I gave this a go upon its release and stopped around the time when the game puts you in Catwoman's shoes. I think I just didn't get in the mood to push further. Playing this again properly and finishing on normal difficulty years later, apart from the minor role she plays in the storyline, I don't really see the need for her to be added to this as it doesn't really offer that much of a different gameplay experience compared to using Batman. The other major thing that irked me whilst playing this was the backtracking, which is a usual bugbear I have with video games.
Compared to Arkham Asylum, the extra freedom is great, and was something that I wanted to be implemented from Arkham Asylum. There is a lot less detective work to be done in this from memory as well. Playing this after Origins, I can definitely see the complaint people had with Origins being too similar but there are some things Origins improved upon such as moving from rooftop to rooftop being faster, fast travel, bigger world, better story, and so on.