I love crossovers where the characters don't suddenly (and usually inexplicably) become close confidants and learn each other's secrets. I also love it when there's at least a touch of the 'unreliable narrator,' where the significance of lines like "Lucius prefers to remain as unaware of when and how I play as possible," Wayne drawled, placing the faintest stress on the word 'play,' is easily spotted by the reader, but lost on the narrator.

Also, the closing line, He owed Bruce one, lying bastard or not, is so very neat.