-The Legendary difficulty setting featuress new dialogue not heard in other modes. For example, after being massacred by a force of Grunts, Jackals and Elites, one of the Grunts asks, "Can I have his helmet?". Also, your fellow Marines seem to be a bit more chatty (as well as profane).
-Under the Legendary difficulty setting, view all of the first FMV sequence. During the sequence, the General says things much differently when compared to the sequence under the easy difficulty setting.