2K Games says the extension will open up new areas of Empire Bay for exploration, including "a train station, the cathouse, a boat yard, a seasonally changing lakefront and some never-before-seen buildings in Empire Bay." It'll also feature new clothing, 20 more Playboy collectibles, and more period 1940s and 1950s music.
So it sounds more substantive than the preceding two DLC packs, and Mafia II was a very strong game up through Vito's incarceration. While it would have been nice to get this on the main disc, those with a Mafiosi fix should give it serious consideration.
The extension will cost $9.99 on PlayStation Network, 800 Microsoft Points over Xbox Live.