I'm greatly enjoying this anime, of course that might simply be because I like these genres.
The original story is written by someone who obviously has a great understanding of the MMO genre, and he incorporates the concept into his story very well.
That being said, one does not have to be a fan of MMOs to enjoy it. Rather than focusing on the gaming aspect of MMOs, it focuses on the people involved.
I really enjoy the development of the characters. The main protagonist is not one of the "instant super hero" (which some people seem to prefer), which leaves a great deal of room for character development, something I greatly value in stories. This also makes the choices done by the protagonist feel natural.
The inner conflicts which the people involved face have been well thought through and, most of the time, I agree with the way they choose to solve them.
The story is -very- good at portraying some characters as sympathetic and others as unsympathetic so it's easy to take the protagonist's side when it comes to his choices.
If you feel like some of the parts don't make an awful lot of sense, I recommend reading the Light Novels first, as those cover what you might be missing.
I'm a big fan of the animations in this anime. Some of the faces the characters pull every now and then are rather humorous, but this goes well with the story, since SAO is said to enhance character emotions to a certain degree. There are a few points at which the animators have chosen a very curious approach to some of the situations, such as the first-person views, and the in-game lagg/"bugs", but these work very well and truly bring across the "feelings" and atmosphere of the light novels.
They've got Yuki Kajiura. I have the songs of this anime on repeat while I'm writing this.
I think the voices have been very well done for the characters. The voice actors really manage to bring across the feelings and inner conflicts of the characters.
Relation to the light novels:
As of writing this, the 15th anime episode has been aired.
The first couple of anime episodes focus on the events prior to the start of the first book out of the light novels.
Along with this, all of the side stories which appear in the second book (aside from one, which appears later) have been packed into the first 7 episodes of the anime. Among these is also a new one, which I have not read in any of the light novels.
Once the anime reaches episode 8, it closely follows the story of the first book.
The first major "arc" in the light novels appears to end with the 14th episode. From episode 15 onward, the second major arc begins.
All in all:
I think most people would enjoy this story, if not the anime then at least the light novels.