well ill share some of my knowledge although most of u no wat im about to say,,,
Campaign: The Game starts off six months after the detonation of the lightmass bomb. The Locust have found ways to bring down entire cities at once, in big sinkholes. The story will also focus on Doms quest to find his wife Maria, who got lost after emergance day.2 new characters added Tai and Dizzy.. Tai = badass Dizzy = cowboy... Carmine does in fact come back... Get to face brumak (big lizard thing with a even bigger GAT) Rumors of riding a brumak. New enimies new levels gonna be a real good campaign. will be much longer and have more in depth vehicle controlling and more vehicles. at least 2 new kinds of locust including locust priests. Casual is much easier while Insane is much harder. when doing co-op each player can select their own difficulty (only 2 players tho =[ ). more interactive cutscene camera
Multiplayer: New HORDE mode in which u can fight a seemingly endless stream of locust with a party of friends to achieve high scores. Multiplayer will run on a trueskill system so u are playing kids around your level. U CAN PARTY UP WITH YOUR FRIENDS FOR RANKED MATCHES.. will have playlists of 10 game modes such as SUbmission, Wingman and guardian as well as classics like warzone and execution. Veto system will not exist .. however b4 a match begins u choose between 2 selected levels.. most votes wins.. if none vote or a tie happens a random 3rd one will be played..Bots (computerized multiplayer-like enemies) will be in the game for either offline activity or to fill in needed spots in unranked games,, Return of levels such as gridlock but with additions such as RIVER. Wingman game mode = 5 teams of 2 each 2v2v2v2v2 Assassination = Guardian but with a twist??? u will keep respawning until ur leader is dead. meat flag.. ccapture the flag but with a human body. all modes 5v5. when dead can fly around map on a new camera which can be used to take screenshots. getting damaged slows u down. can choose wat gun to use b4 matches Lancer or hammerburst (i dont believe but ma sources so far have done me good). levels are larger
Guns: same guns but with upgrades and some new ones... Poision Grenades kill opponents instantly and slowly detoeriorate anyone who is near the blast... smoke nades stun now,,, can take nades to walls for "TRAPS" Hammerburst is now semi auto. Gorgon pistol with a 6 shot burst and when u hit someone with a bullet it leaves a trail of blood so it is easier to follow girls who run away =P.. Specific melees and exections for each weapon. chainsaw dueling but people who are chainsawing can be wounded or die while sawing. Shields that can be used as a portable cover but can be destroyed if an oppent approaches it too closely. Active reloading is much different from gun to gun. a flamthrower aka "SCORCHER".
If i find out anything else or if you have any questions post here or talk to me on aim... my sources are IGN. Gamestop. Gamespot and epic games.. all on internet and sum of e3 interviewing =]