Here's a breakdown:
Xbox360
Full HDTV support, every game WILL support 720p/1080i widescreen as a minimum requirement (but it will still be compatible with standard TVs)
Full Dolby Digital support with increased surround sound abilities
Can read all disc formats: MP3 CDs, CDs, DVDs, CD-Rs, everything without buying anything extra to play them
Built-in media extender: it will stream MP3s, videos, and picture slideshows from your PC
MP3-player support: it has a couple USB ports on it which will allow you to transfer music to and from your Xbox to your MP3 player. You can also use your custom playlists on your MP3 player as custom soundtracks in games
Digital camera support: you can transfer pictures to and from your Xbox to do anything from watch slideshows to customize your Live homepage. Microsoft will also release an "eye-toy" camera that will allow you to put yourself in the game. Perfect Dark Zero will let you take a full body shot and use that as a skin in online multiplayer
Built-in 20GB removable/upgradable hard drive
Interchangeable front faceplate (kinda lame, but better than nothing, at least I can change it to black from the stock "iPod white")
Fully wireless controllers and wireless Xbox Live headsets. USB 2.0 ports on the front and back allow for wired controllers to be used also.
Optional remote to integrate further with Windows Media Center Edition (with remote power shutdown) Shutdown and media controls are also accessible with the controller
"Always Connected" Live interface. Every Xbox comes with Xbox Live Silver installed. It will give you access to everything Live users have except online play. Xbox Live as we know it will be expanded with deeper customization features and stat tracking in the Xbox Live Gold plan. The Xbox Live screen can be accessed at ANY time and it drops down and covers half the screen, even while playing a game, so you don't have to exit out to download content or talk to Friends.
As far as graphical abilities go, it is THE most advanced piece of gaming hardware on the block. I know specifics might not mean much to you, so take my word for it: the power and technology in the Xbox360 is beyond anything available now or even in the next year. Supposedly, Microsoft is planning on selling it for under $300, so it will either be $250 or $300, which is amazing.
Games shown on the MTV event last night:
Perfect Dark Zero looked awesome with the wide variety of weapons, 50+ online players, completely custom multiplayer characters, online co-op, online counter-op, and some stealth moves. After seeing what I saw, I'm even more convinced that it will rule.
Kameo: Rare's bastard love-child which almost made it to Xbox before being delayed for Xbox360. There was a scene of the hero charging through a field of hundreds of enemies on the back of this badass-looking unicorn. It should be a great fantasy-action game.
NBA 2K6: dude... the absolutely most insanely PERFECT human animation and photo-realistic graphics. It was unreal.
Gears of War: speaking of Unreal, this game uses the latest Unreal engine and it has the most detailed and freaky looking beasts and environments I've ever seen.
Project Gotham Racing 3: Destroys the line between realistic-looking and reality
The Darkness: creepy looking game with "sweet" written all over it
Ghost Recon 3: the most realistic-looking military shooter I've ever seen. It was a full-scale urban battle with more detail than you'd think is possible
Call of Duty 2: as real as Ghost Recon, but WWII setting.
Saint's Row: it was just a clip of a mean-looking dude crashing his car through a police baracade, I'm guessing it's a GTA knockoff. It kind of had its own look though...
EA (yawn) showed some video clips of Madden, Tiger Woods, and Need for Speed and they seemed kinda lame. Lame might not be the right word, but they were obviously rendered video rather than actual game footage.
E3 starts next week, so most likely all the remaining details will come together and a LOT more games will be shown. All I know at this point is that everything is turning out BETTER than expected.
Here's a great summation article from Tom's Hardware:
http://www.tomshardware.com/game/200505121/index.html
TeamXbox.com has much deeper information.