Yeah I haven't tried the challenge modes yet, but so far it seems like just a really awesome rental, unless you enjoy replaying single player games a lot. I don't, lol.
But other than that no complaints at all, really. Jay you'll be happy to know that you're not at ALL constantly jumping back and forth between gargoyles, it's constantly switching up who and what you encounter, so you never really get bored of one aspect. As the reviews said, it's very well paced so far, I couldn't be happier with that aspect of the game. I'm not bored of the combat yet, mostly because while the counter window is large, so is the recovery on a lot of your moves. Forces you to stay sharp and not just mash it all out. You can also get an upgrade for JF attacks.
So far not a lot of true boss fights, Scarecrow sections were awesome but not really a boss fight. Only one real "boss" fight so far, won't spoil who. A good chunk of the villains seem to be represented in the environment itself, as opposed to "Batman vs so and so." Just got up to the Gardens before work today, between the trailers and being totally obvious, it's really no spoiler as to who's next lol.