Sure, I'll try by using my own experience watching it.
Sword Art Online is incredibly interesting. It combines futuristic sci-fi with medieval fighting styles. Even better, it's a well-done action/romance anime. While shounen fans are happy with the awesome fighting and setting, the shoujo fans get what they like too. I admit, I liked the 1st season far better than the 2nd, but the anime as a whole was absolutely amazing.
I enjoyed the character development and setting also. Not only do almost all of them have 2 sides to their personality (It's a given, you'll find out if you watch it.), but they also are very interesting to watch. Even the filler-like arcs were entertaining. Each of the characters brought their own personality into their fighting style.
The last thing I enjoyed was the complex physical setting. As stated in my first paragraph, I liked this a lot. The fact that a virtual-reality online gaming world where people's lives were at stake is reallllyyy cool in my book.
I don't want to ruin or spoil anything beyond the first episode for you, but I highly recommend SAO. It was fun to watch, and I hope you think so too.