*WARNING: THIS IS A REVIEW AND MAY CONTAIN SPOILERS. IT'S RECOMMENDED TO READ IF YOU KNOW ABOUT SWORD ART ONLINE ALREADY.*

Sword Art Online is a great Light Novel and the anime is also a great watch too. There is also the manga of Sword Art Online: Aincrad, which on the other hand is not too great. I'll tell you exactly why.
This manga would deserve a 7 compared to the Light Novel or anime. Many people take a 7 as a relatively low score, but it indeed is pretty high. I've read parts of the LN and I'm watching the anime. I will review and compare this from the anime, since it was nicely adapted from the LN.

The manga was good, but it lacked in many things, that the Light Novel and anime provided. This is what I mean when I say the manga is not as great compared to the LN or anime.
From any Sword Art Online fan, the basic story is about a boy named Kirito who gets trapped in the game Sword Art Online. If you die in the game world, you die in real life. The only way to escape Sword Art Online is to beat all 100 floors.
Based from the anime, the events that Kirito is involved in occur in the manga as well. Events such as, how the start of the was game, how Kirito joined a guild, or how Kirito met Asuna are all in the manga. The manga's tells of all these events, but they are presented not as great as the anime or LN did.
The story is overall the same and very good, except that the art, plot development, and character development bring it down a bit.
The art is not very good, and it is hard to tell what's happening because the art is very high quality. It sometimes gets a bit sloppy during the fighting sequences and is no match compared to the anime.
The character development is also something that brought the score of it down. A lot of the material and scenes feel rushed, on the other hand the anime and LN have much better pacing.
Also the lack of explanations bring the score down as well. From the anime there is an episode about Yui, the child that Asuna and Kirito found and started to care for her, is also included in the manga, well part of it. This is also apart of the Ln as a well written side story. There was about a page that showed Yui in the manga, but did not explain who or what she was. The only reason I knew it was Yui is because of the anime and LN. For any reader who hasn't watched the anime or read the LN, would most likely be confused. The manga is not fully updated online, but even if they put an explanation in, it would have been better to put it in at the time Yui was shown and not later on.

Overall, if you are a fan of the Light Novel series or anime series, and you can't get enough Sword Art Online, then I recommend you read it. If your just a regular fan reading the LN or watching the anime, then you might not find the manga as great. It's an okay manga on it's own, but compared to it's other versions, it's not as well done. To be honest, the LN and anime gives you a thrill when you read/ watch it, the manga sadly doesn't give the same feeling.

NOTE: I WILL UPDATE THIS WHEN THE MANGA IS UP TO DATE ONLINE (10/23/12)