The patch will add a new multiplayer mode -- Meltdown -- as well as a new difficulty setting for co-op play. This will give higher EXP rewards, but will be much more challenging. Finally, the patch will also allow a local co-op player to sign in with his PSN profile, saving his accumulated scores.
As for the paid content, there are a number of maps being released which have been designed to allow more intimate, small scale battles. The Aftermath map pack will cost you $5.99. There are also a number of skins which will be purchasable for $0.99 each. For more details and footage of the maps, check the video after the break.
[Via Just Video Games; Thanks, Alexandra]