Addressing one of the biggest complaints with two, Resistance 3 returns the weapon wheel from the original game, giving you access to your full arsenal instead of having to choose two guns at any time to run with. Weapons will also be upgradeable this time around. How that will work wasn't mentioned; though, the story does say that they will improve as you continue to use them. This makes it sound like the weapons will accrue some sort of experience points.
A couple brief mentions were also made of multiplayer. The team is hard at work on full two-player co-op throughout the main campaign--playable both online and split-screen. They're calling the multiplayer "progression-based" which most likely means it will take cues from the popular player development system used in Call of Duty and similar games. As one of the captions for the art notes, many of the multiplayer maps are set in locations not in the campaign, but places that will have been mentioned or otherwise connected back to the main game.