First thing anyone should know is that this series is the direct sequel to the first series, Shakugan no Shana. It is highly recommended to watch that before watching this series. The first series explains terms and sets up the characters for this series and a viewer will be much less confused as to what's happening because this series derives directly from what happened in the first series.
That being said, if someone's already seen the first series, then they know the story of Shakugan no Shana Second already, for the most part. Nothing's changed from series to series. Yuji Sakai is still a Torch and a Myste, and Shana is still a Flame Haze. Together, they are tasked in killing Crimson Denizens (Guze no Tomogara) who live in the Crimson Realm, the parallel universe that lies directly on top of the human world. There is little change to setup and the second series continues this trend. As expected then, most of the plot that drives the series along is focused on different Tomogara who show up at any given time and Sakai and Shana have to fight them off with assistance from their close friends.
If you had any questions from the first series (you probably did) and were expecting answers. Well, the series may answer one or two, but you'll probably find yourself asking more questions by the end and you'll have to watch the next series to see if it answers your questions (It probably won't). There's not much more to add here other than the show does a good job of continuing what was started before and it introduces new plots and ideas that certainly build on the old.
But Shakugan no Shana never really was about the strong story, was it? The characters are what make this anime shine. All of your favorite characters are back. Margery Daw, Wilhelmina Carmel, Kazumi Yoshida, Keisaku Satou, Eita Tanaka, Hayato Ike, and Matake Ogata all share a large portion of the show and the series mostly devotes its time developing these characters. Every character develops in their own way and that's the enjoyable part of this show. You find yourself attached to the characters as the anime goes on and as different situations happen, viewers become emotionally involved.
That's where the strong point of Shakugan no Shana Second lies. The characters are all widely varied and they are all shown to have different thoughts and beliefs about what is happening in their lives. Different characters take different paths and not all of them are remotely close to what you might think they would do. Characters face turmoil and difficulty and are forced to make difficult choices. This makes the characters of Shakugan no Shana Second incredibly strong because the creators made sure to continue building them from the first series. They all change in some way or another and watching them change is the real joy of this show. There is hardly a dull moment in the show as a viewer will care in some way about every single person on the screen at any given time.
Animation is, of course, fantastic. All the characters are uniquely designed, every model looking different from the other. Fight scenes flow smoothly, and detail is incredibly high during intense moments. Shana's flame looks as detailed as it did the series prior. There are some moments where CGI is clearly used and it detracts heavily though. It's usually in the middle of an intense sequence of events and completely throws off the feel of the moment, which is a shame. Other than that though, the only other issue is that the character's eyes are rather large and they seem slightly too far apart from one another, but after some time one gets used to it.
The soundtrack is great as well. The soundtrack always sets the mood and accompanies scenes exactly right. During suspenseful action sequences, the music pumps out fast beats and matches the mood, while during a slow, emotional scene, the beats drop away to something more soft and quiet, drawing the viewer into the moment intimately.
There's not much to be said negatively about Shakugan no Shana Second other than the rather disjointed plot that is really only there to drive the strong characterization of the characters. There's nothing deep or meaningful to be said in the story, but in reality, that doesn't matter in this show. Plot comes second to the strong characters that are the driving force behind what brings the viewers back. When a show can get a viewer to invest emotionally into its characters, then you know that a show is doing something right.
