Like everyone else, I was blown away with the Scarecrow encounters (made me want to replay Psychonauts). After his first boss battle, I thought the side-scrolling/giant Scarecrow thingy was brilliant and I couldn't wait to see where they would go with the next inevitable encounter. Sure enough, your next two run-ins with him have even better introductions, but unfortunately the actual fights with Scarecrow are identical to the first, which was a huge disappointment. I was certain they would run with the creative possibilities, but they simply repeated the first idea. Twice!
It sounds odd, but for me, Scarecrow is both the highlight of the game its biggest disappointment. Even moreso than the Joker battle.
Having said that, B:AA is still the most fun I've had playing a game in a long, long time.