Debut Trailer here!
From the Fallout Wiki.
The game is set in a post-apocalyptic, retro-futurist Las Vegas following the Great War between the U.S., China and other countries, a conventional and nuclear war that occurred on October 23, 2077 and lasted less than two hours despite causing immense damage and destruction. Before the Great War were the Resource Wars, during which the United Nations disbanded, a plague rendered the United States paranoid, and Canada was annexed. The city of New Vegas itself didn't get hit as much as other districts, and most buildings were left intact. Hoover Dam supplies all the free electricity and water to those who control it.
Story
The story will continue some parts of the Fallout and Fallout 2 stories, but will not be related in any way to the one in Fallout 3.
Fallout: New Vegas will take place in 2280, 3 years after the events of Fallout 3 and 39 years after Fallout 2, making this installment set the farthest in the series. The New California Republic will play a major part in the story, in a three way struggle between the NCR, the Caesar's Legion slavers, and the local New Vegas populace.
The player will play as a courier, who was left to die in a shallow grave, rescued by a TV Robot named Victor, and patched up by a Doctor Mitchell.
The gameplay system will be similar to the Fallout 3 gameplay, although some changes have been made.
Hardcore mode
Hardcore mode will be an optional setting which makes the game more realistic with things such as dehydration and healing over time.
Normal - Weightless ammo, Instant health from stimpaks and no dehydration
Hardcore - Ammo has weight, Stimpaks heal over time, and you must drink water to prevent dehydration
Character system
The SPECIAL system returns, and directly influences speech options and quests. Like in Fallout 3, perks are gained every level.
Combat
The Vault-Tec Assisted Targeting System, or V.A.T.S., is an active pause combat system implemented in the game, just like in Fallout 3. While using V.A.T.S., the otherwise real-time combat is paused. V.A.T.S. also allows the gory deaths in the game to be shown in slow motion and great detail. Attacks in V.A.T.S. cost action points, and the player can target specific body areas for attacks to inflict specific injuries. Unlike Fallout 3, melee weapons now have special moves in V.A.T.S., such as "Fore!" for golf clubs.
Karma and Reputation
Karma is back, but now incorporated alongside a reputation system, similar to Fallout 2.
Weapon Modding Feature
This modding feature allows you to modify your gun by adding things like scopes, extended magazines, etc. You are able to have a weapon with no more than 3 mods attached to it. It is confirmed that these mods will be permanent to that weapon.
And here are some screenshots from the Xbox 360 magazine
Companion Commands
New Enemy Type
New Super Mutant
V.A.T.S Special Moves
The rest can be found HERE
Personally, i'm not too impressed by the graphics, it just looks like a modded Fallout 3... But hey, if it ain't broke, don't fix it.
Should be released Fall 2010
Completed FO3 and all the expansions so stoked for this.
).