Fatal Freight is a 5-chapter campaign which aims to provide gameplay comparable to that of Valve's official campaigns. The levels were designed heavily around competitive play and can be expected to provide a hectic Versus experience.
Extensive testing has been done to ensure this campaign is playable on all difficulties, including Realism Expert. All secondary game modes (Survival and Scavenge) are fully supported by this campaign and most mutations should work with Fatal Freight as well, so have at it!