The pack sounds a little weird when you consider that the rest of Mafia II is a pretty typical open-world shooting-and-driving experience. It's described as "arcade-style," and players will be able to compete on online leaderboards as they run through the Betrayal pack's "dozens" of missions.
Another downloadable offering, called Jimmy's Vendetta, is also briefly mentioned in this morning's release. Unlike the Betrayal missions, Vendetta will be available on all three platforms. Like the other pack, though, Vendetta will offer leaderboards and replayable missions. No release timing has been announced for Jimmy's Vendetta just yet.