Metal Slug XX is a remixed port of Metal Slug 7. The six default characters (that includes two guests from The King of Fighters), seventy combat school missions are still in, and presumably the lite flirting with Cynthia too are in the Xbox 360 version. The big addition is cooperative play, offline and online co-op.
SNK may have other surprises since Metal Slug XX has a downloadable content option in the main menu. Not including any extras, Metal Slug XX costs 1,200 Microsoft Points ($15). Currently, the May 19 release date is just for Japan, but Xbox Live Arcade games tend to be released simultaneously in all regions.