Few concrete gameplay details have been released since the game's announcement, but today the developers did let a few extra details slip.

Highlights:

• Two player online co-op is confirmed for consoles and PC. Console players will also have the option of split-screen co-op.
• Co-op will be an entirely separate mode that will not include the story elements of the single player campaign.
• Hooper mentioned "armor" and "inventory" systems, and indicated that there will be some type of world economy that the player can participate in.
• The shooter gameplay will play out in the tradition of id FPS titles.
• Vehicles are being used as an "extension of the player," allowing users to drive to instances, or race on tracks that are found in each town.
• Racers will have two seats for co-op riding, with one player manning a gun.
• Vehicles can run over monsters, but the gore will be limited, as id is shooting for a Teen rating to broaden its audience.
• Training missions played at racetracks will teach players new vehicle skills.
• Though the world will be large, it is not a sandbox title or traditional "open world" game--players will need to complete the game's story quests in a linear fashion.
• Instances, encounters and items will be crafted, not procedurally generated as in a game like Diablo.
• The game is targeted for release sometime within the next two years--likely in the final half of 2009.

Carmack also took some time to elaborate on how the team is approaching the weapon design:

I really do think that on past projects, I've made these lists of, here are all the possible things that a weapon can do, visually, audibly, motion-wise, all of that. Now it's like, how do we want to apply this to each different weapon to make them work well. Because weapons are still one of things that as you survey first person shooters, there's this clear distinction between the "A" titles, and the "B" titles that just don't do their weapons very well. They don't look good, they don't feel good--they just don't come off nearly as well. So we're definitely gonna make sure that that aspect of it--the tactical, low-level [aspect of] the weapons--will be cool. They'll have their punch, they'll be fun to shoot, and you will have fun as you go around firing your weapons at the bad guys.