First and foremost, if you ever plan on or have considered watching this special, I'm assuming you've seen the first season, otherwise, there's no real reason for you to be here. Because this is a special, my rating for it is not based on complete quality of the special on its own, but how the special relates to the first season. A special is an addendum to a series; it's like an extra episode. Keep that in mind while reading my review.
Examining the special piece by piece, I will start with the basics: art and sound. As I mentioned before, if you're considering watching this special, it's probably because you saw the first season and are interested in seeing similar content. I can assure you that the art and sound in the special is exactly as it was in the first season. Not even the opening theme is new. Simply put, your personal opinion on the art and sound of the first season is going to be identical to your opinion of the art and sound in the special. So because nothing has changed, these two factors can be ignored. The same goes for characters. None of them have changed, so expect nothing different from before.
What really matters is the story, right? Yes. As far as specials go, I thought the story was, in a word, decent. Everything started off incredibly slow; the whole first half of the special was basically recapping some of the more important scenes in the first season with brief bits of character dialogue strewn around in between. It wouldn't surprise me if you said that that sounds horribly boring. You'd be right. It was horribly boring. I can't think of a single person that enjoys recap or flash backs. The only thing that kept everything at least somewhat interesting was the inclusion of some mild fan service. Which, I should specify, although it probably should have been obvious to you, is entirely female only. Having watched the first season, I'm sure you know that this is an anime tailored mostly for males or really anyone attracted to females; I say males because the only real canonical pairing is Kirito and Asuna which is obviously a straight relationship. All of this is to say, there is female fan service, so expect it and appreciate it if you want. Now, while the first half of the special is truly boring, the second wasn't so bad. The rest of the plot involves a quest in Alfheim in which all of your favorite characters take part. Of course before the actual quest begins, there is plenty more fan service. The quest itself isn't really all that interesting. It isn't exactly high stakes as some of the events and quests were in the first season. Overall the quest is laid back. We see some fighting, some humor, some dialogue; really everything you'd expect from a typical episode of really anything. It wasn't incredibly captivating, but everything sort of fit together enough for it to be pleasing.
Looking at this special as a whole, I would say that it was pretty good. As you can probably see, I gave it a 7, which I think is a generous score, but not something it didn't deserve. It really and truly is an extra, fun episode involving the characters of Sword Art Online doing things you never got to see them do in the first season. If mundane events where nothing really happens don't appeal to you, I wouldn't bother watching it, otherwise I think it's at least worth the watch.