Every feature, every complex ballistic calculation, every campaign and every mission ever designed for the series has been ported to the console, optimised and improved for the Xbox hardware.
BIS must have spent a whole sea of money on porting every campaign ever designed for OFP to the XBox.
edit: Oh, and this nearly made me cry ( ):
quite a few Xbox only graphical touches have been added to the mix such as Depth of Field (variable camera focus effects) and High Dynamic Range Lighting (a more realistic method of simulating light sources in games).
So that means no HDR for ArmA? Or is it just compared to good ol' OFP2001?