I'll keep this review short and sweet.
Story - Isnt much to tell reall. While there are similarities to Sword Art Online (and even references to some of the gear used in it) the story seems a little shallow. But it leaves a good foundation that can be built upon in future seasons (If there are any :p)
Animation - One of the best ive seen.
Sound - Music wise it doesnt even compare to a series like Macross but its decent enough to keep you entertained. Supporting sounds are execellent.
Character - As with the story all characters have a strong foundation built upon during season 1 which leaves huge potential of a full character development in future series.
Overall - Not supriceed that this is one of the top animes out there. While it lacks in Story and Character it makes up with Animation and sound. A must watch for true anime fans.