MP video for FREE ROAM mode here...
http://www.youtube.com/watch?v=AvBhPAMDUAQ
Entire world is the "lobby" for multiplayer free roam.
Go it alone or form a posse of up to 8 players. Your posse can take on criminals, the law, or other player controlled posses. Many events and challenges in free roam.
Go hunting together. Structured events like traditional deathmatches can be engaged in.
Doing things builds experience (of course) and there are 50 levels to rank up through in free roam. As you rank up, you gain better weapons, abilities, horses, etc.
Many more structured multiplayer events will be revealed later. The next reveal will detail the competitive modes.
IGN impressions (details some competitive modes)...
http://ps3.ign.com/articles/108/1082538p1.html
AWESOME.
Rather than tossing you into a map at random spots, Red Dead Redemption starts with an old-fashioned shootout. Each of the up to 16 players starts in a circle. When the countdown ends, smoke and lead fill the air. The last person or team standing then gets to run off and grab some pickups and camp out at a favorite spot while everyone else has to wait to respawn.