Insomniac Games has announced that Resistance 3 will have a co-operative campaign that will be much more similar to the first iteration of the game than the second.
This means that it'll be a two-player affair, and that you'll be able to play it local split-screen. However, an online option will now be available - something that was missing in the original.
They also announced that the multiplayer in Resistance 3 will be much more focussed and that weapons will now be upgradeable based on how much they're used.
The first ever gameplay footage is expected to be shown off at the 2010 VGAs.
Source: PlayStation Blog