Today, Insomniac Games announced their Brutality Pack for Resistance 3. This pack includes a new co-op mode, a sledgehammer melee weapon and some songs to pump you up.
The Brutality Pack biggest addition is the online and offline co-op mode where you and a friend works to survive waves and waves of Grims. This is sorta like a zombie mode / horde mode combo. The DLC also features the sledgehammer from the single player game and it becomes usable in all the online modes. They are also adding in another multiplayer skin, Mick Cutler, and a PS3 static theme.
The coolest part of this update is the inclusion of songs from the metal band Mastodon. Apparently, Ted Price, president of Insomniac is a big fan and managed to get some instrumentals and full songs as background music.
The DLC is $4 and is on the PSN now.