I judge an anime based on some aspects: story, artwork/animation, characters, and sound.
Sword Art Online started really well. A good story always retains its original elements seen in the beginning. Here I was expecting a survial story like Gantz but in a fantasy setting. Instead, SAO left from its original roots and focused on side stories and characters that do not have any relevance to the overall plot. It got worse as the anime continued to in the second part. What turned into a story about survival ended up turning into a convoluted mess in an attempt to try to justfiy what is going on. The story uses lots of plot devices and haxes that are in favor of our protagonists. Not to mention, that as the story progressed, it resorted towards harem anime cliches, unecessary fanservice, incest, and tentacle rape.
The background settings in SAO are good looking. Although they do show some typical fantasy setting in regards to the towns, some of the environments themselves were interesting, especially with the world tree in the second part. However character designs are typical but they at least look okay to good looking. The only problem is that judging by what they character looks like, you can instantly know what kind of person that character will be. Not to mention there are some disruptions and recycled cells in the animation. Other than that, SAO's artwork/animation is decent.
Characters in an anime can make or break an anime. In this case, it broke, bad. The characters in SAO were by far the worst part of this show. The only reason I do not give it a 1 out of 10 is becuase they decided not to do a wimpy protagonist for once. Our main hero, Kirito, is the next Kira Yamato (Gundam Seed). He's a gary stu. In the anime Kirito is perfect, he wins effortlessly, he is a walking deus ex machina, all of his fights are anti climatic becuase he is so overpowered, and everything he does is right and everything that everyone else does is wrong. Not to mention that most of his interactions are with female characters that only add to his growing harem. In reality, he is just a self insert character for otaku to live out their fantasies. Asuna is just as bad, if not worse. She is mainly in show to appeal only to the audiece as their waifu. She cooks, she cleans, she is attractive, a tsundere, and she is the second most overly powered character other than Kirito. The romance is superficial considering that they barely knew each bother before Kirito proposed. Still a better love story than Twilight though. Your side characters consists mainly of moe archetypes, cliche villains with lame motives, an incestal cousin, other girls to add to Kirito's harem, and other male characters who are not given much of a background and only there to make Kirito look more awesome.
The voice acting is decent in SAO along with some of the sound effects. The OST are composed mainly by Yuji Kaijura, who did some of the music for anime like Pandora Hearts or Madoka Magica. The themes are not bad either. So the osts are pretty good, one of the few saving graces of this anime.
What would have been a great anime if they had they stuck to the original storyline and not fallen into a typical harem anime, SAO would have been much better. Overall, I give Sword Art Online a 5.5 out of 10.