Shakugan no Shana isn't one of my top 10 anime of all time, but it's a solid series that provides a mix of action, drama, and romance with interesting characters set in a complex world. Based on a series of novels and animated by J.C. Staff (Mahoraba, Karin, and many others), Shana is coming to Region 1 DVD in September, and that DVD is sitting in a slot on my Amazon wish list.
The main characters in Shakugan are Shana herself, who's kind of like Rebecca from Paniponi or Hazuki from Tsukuyomi--she's under 5 feet tall, confident in her abilities, and not likely to win any awards for being Miss Congeniality. To give a brief summary of the plot, the world we live in isn't as it appears--people are being killed by monsters for their power of existence, and to keep the rest of us unaware and avoid too much disruption, those who are killed are replaced by "torches", which slowly fade away over time. Flame Hazes like Shana fight these monsters to preserve the balance of the world. Yuuji, the other main character aside from Shana, finds out that he himself is a torch--but he has a special power that makes his torch regenerate nightly so he won't disappear. The catch is that power makes him a target, because a lot of other people want it--so Shana reluctantly ends up staying by his side.
What makes Shakugan no Shana fun to watch, for me anyway, is the interaction between Shana and Yuuji and getting to see both of them grow as characters, especially Shana. Shana starts the series with no proper name, just a title as a Flame Haze, and she dismisses Yuuji as "just a torch" and someone who's not really alive at all. But Yuuji gives her the name Shana and that starts her on the road to becoming more human. Shana's a lone wolf at the beginning, but by the end she's found more to care about than her mission as a Flame Haze, and she's become a much more balanced character. She doesn't turn into a Belldandy clone (thank God/Haruhi for that), but her character gets some real development and change during the course of the series. Her and Yuuji get a few memorable scenes, and Shana's trademark "urusai, urusai, urusai" gets a little old by the end, but is good for a few laughs.
A lot of people criticized Yuuji for his reaction to the events in the first episode, but I think he actually handled it pretty well--not many people would jump between a total stranger and someone swinging a sword, most people would have just run like hell. He starts out pretty much useless in combat, but as things go on, he learns more and works hard to be useful to Shana, not just wanting to be a bystander. In the middle of the series, his lack of decisiveness over the whole Yuuji-Shana-Kazumi triangle can be annoying to watch, but given everything else he's been through, I guess I should cut him some slack.
Over the 24 episodes of the show, there are a few story arcs involving different bad guys--the final arc doesn't really get tied up neatly by the ending, although there's a movie in the works so maybe that will close out the arc. The bad guys are an odd bunch--there's the guy who has a doll fetish, the siblings who french kiss to exchange power, and so on. They're pretty much one-dimensional and just generally evil, with no real backstory on any of them. But some of the side characters stand out--Iwata Mitsuo is awesome as usual as Marco, the sidekick of one of the other Flame Hazes, and with 24 episodes to work with, the side characters get their chance to shine in the limelight. Kazumi, Shana's rival for Yuuji, has her fans, but she comes across to me as a drama queen, getting way more worked up about Yuuji than anyone in their right mind would. She also seems to have the "my only purpose in life is to make bento and someday become the male lead's girlfriend" syndrome you often find in anime girls, which just makes me want to roll my eyes--but fortunately she's not in the spotlight nearly as much as Yuuji and Shana.
The pacing of Shakugan no Shana isn't for everyone--people looking for Inuyasha-like action will probably fall asleep at several episodes of Shana that are 90% plot exposition and dialogue. There are long periods where nothing is going on but the characters talking, and for some people that's a big turnoff. That wasn't a problem for me personally--the world in Shakugan no Shana is complex and they throw around a lot of terminology specific to it, but the mostly-dialogue episodes still held my interest and were a good break from the action. There's also some Shana and Kazumi service thrown in throughout the series, but it's not like Girls Bravo or anything where it gets distracting.
Overall, I think Shakugan no Shana's a fun series to watch. It's hard not to like the melon-pan eating heroine, and the short special episodes (3-minute extra shorts that came with the R2 DVDs) are especially hilarious. I'm looking forward to the movie and hoping to see Kazumi get smacked down so Yuuji can end up with Shana ;)