What an amazing anime. I've only watched about 5 episodes but it has made such an impression on me that I can say now it's one of the best anime I've seen.
The premise is that 10 years from now, a new virtual reality MMO called Sword Art Online comes out. The creator of the game then traps everyone in the game by removing the logout button and sets it up so that if you die in the game, they die in real life. And if someone tries to remove them from the hardware they will die. The only way to leave the game is to beat it. It focuses on one of the beta testers who spends his time between the front lines of the game and helping lesser players in lower areas.
As someone who has played MMO's for a long time, they really nailed some of the characters types you find in MMO's. The fact that death is real here makes for quite a few dramatic moments. It can be very tense and very sad at times.
My only lingering question is how is everyone getting their basic needs for their real bodies since they can't survive on virtual food and drink and such. However, I have read that does get explained later in the show.
I highly recommend to any one who like anime as this has a little bit of everything in it.