Not your typical run of the mill DLC here, seems like R* are packing quite a lot of stuff into this. The press release also confirms a 17th February release date, and states pricing information and more details will be announced "soon".
The Lost and Damned features a new main character and plot that intersects with the storyline of Grand Theft Auto IV; new missions that offer an entirely fresh way to explore Liberty City with new multiplayer modes, weapons and vehicles; and a diverse soundtrack with additional music - all with the incredible production values that are the trademarks of Grand Theft Auto.
Rockstar released alongside this the first screenshots of episode 1 of the downloadable content, The Lost and Damned. Of course it's running on the same game engine so no improved graphics or anything to look at. Also released was the logo for the episode, click that thumbnail for a stupidly high resolution version.
GTA IV DLC screenshots