Resident Evil: Revelations' co-op multiplayer trailer.
While Revelations is focused on the single-player experience that RE: Mercenaries lacked, it features a Raid Mode in which you can work together with a friend to get through special stages (apparently it also has a separate Mercenaries mode). This mode has both local and online support, a store, Chris and Jill as playable characters, and customizable weapons.
Joystiq has more details on Raid Mode and impressions on playing it with the “Circle Pad Pro” add-on:
“Revelations is far more enjoyable with the added analog attachment. The Circle Pad Pro itself feels great; it’s light and contoured for extended play sessions. The extra bulk of the dock isn’t a deal breaker – at least, it wasn’t once I got my hands on it. Seeing it is one thing, but once I actually used it, I was sold.
Revelations has a specific Type D control scheme, tailored specifically to the Circle Pad Pro. I didn’t need to set anything, though you can calibrate the extra stick. Controls are re-mapped to the Circle Pad Pro’s four shoulder buttons, so you don’t have to worry about moving your hands back over to the 3DS, unless you want to use the touch-screen.”
I’m glad to see that Circle Pad Pro controls don’t seem rushed, given that the new accessory was introduced so late into Revelations' development.
Preorder: Resident Evil: Revelations