The Section 8 forums have some info on the new DLC. It's three new maps and ten achievements, which can be purchased in-game via the downloadable content menu. It's 560MS points, which is around $7, which seems like a lot to me.
The Seek and Destroy Map Pack expands the Section 8 experience with three new maps for the Multiplayer and Instant Action game modes. Players fight for control of a geothermal energy plant on the salt flats of New Madrid in “Devil’s Backbone” and battle in the narrow confines of a hazardous valley on the planet Titan in “Hornet’s Nest.” “Azure Basin” is set high atop a mountain plateau where a massive hydroelectric dam sits astride the map, with combat ranging both inside and outside of the facility.