Well, it did feel like Shakugan no Shana all over again. However, I liked it better somehow than SnS (not to say SnS wasn't good).
First of all, Louise was more likeable than Shana for me.
I perceived Saito as a far better lead than Yuuji.
Some gripes I have : The series is too short. If Shana got 24 eps, movie and plans for second seasons, I don't see why ZnT couldn't get more novels, therefore more animated stuff. I liked the somewhat lighthearted premises more than the brooding SnS world. And damn, while I think Louise is nice, AGAIN (as was obvious), the male lead doesn't end with my girl of choice (Kazumi or Siesta)... Oh well... I guess it can't be helped.
I fel the whole conspiracy element was rushed and not developed as much as it could, but you can't do much in 13 eps.
The last episode was as enjoyable as the rest, although I'd want a bit more of an epilogue, it was still in the spirit of the rest of the series, so no gripes about it. It was a good ending.
Overall, it was fun, not the best or anything groundbreaking, but I'll certainly watch a second season if it ever comes out.