Manga One of anime's overlooked gems
NOTE: I have not finished the series and my opinion may shift when I do.
Shounen action is one of manga/anime's most formulaic and familiar genres. Thus it is hard for newcomers to the field to really distinguish themselves, especially when they have a setup as generic as Kekkaishis. (Read the plot description; it doesn't exactly sound revolutionary, does it?) Furthermore, it's generally set apart by its loudness and brashness. Think of shounen action and you think of roaring, heart-pounding combat like Fist Of The North Star or Dragon Ball, stylish gangster-influenced attitude a la Bleach, plucky hyperactive youngsters like Luffy and Naruto, maybe something offbeat like Soul Eaters macabre art design.
Kekkaishi doesn't boast any of that. Its protagonist, Yoshimori, is neither Hot Blooded nor naive/innocent. But ultimately he's just as endearing due to his unique combination of sincerity, good humor, quirky personality, determination, and genuine warmth and compassion. He's tasked with inheriting the family business, and isn't entirely happy about it, but he accepts his task without much complaint. His counterpart, Tokine, gets a little mean sometimes, but overall she's awe-inspiring in her cool knowledge and calm demeanor. The two make a great Battle Couple and (in my opinion) one of the most adorable couples in all of anime.
The rest of the show is dominated by this restrained yet effective storytelling. The Kekkaishi are Barrier Warriors, so battles emphasize strategy, agility, and "thinking outside the box" (literally!) over brute force and copious screaming. It's easygoing enough that the characters do their duties while attending school, yet taxing enough that Yoshimori definitely stresses in some fights.
Some have accused the show of being boring, and it's definitely not flashy, but I find the restraint and thoughtfulness Tanabe exhibits very refreshing and endearing. None of the characters are annoying (with the poooossible exception of Yoshi's grandpa), none of the battles are over-the-top, and the animation and art are good. Even if you've "been there, done that" with shows like Bleach or Yu Yu Hakusho, give Kekkaishi a shot. It just might grow on you. (I was hooked from the first episode.)
Manga Brilliant deconstruction of the Shonen storytelling archetype
Kekkaishi is a manga about Yoshimori Sumimura and his neighbor, Tokine Yukimura. During the day they go to school, take chores and train so that at night they can protect the school from demons who try to abuse of the constant spiritual energy emanating from it to grow strong and mighty.
...If the manga sounds boring and same-y from the above description, please hang around a little longer. I still have about three hundred and twenty words to convince you otherwise.
After the (painfully) slow start, it starts to become clear just how many tropes and clichés from traditional Shonen stories are Subverted or even Played For Laughs throughout the story. The title character, Yoshimori, stands far away from the Idiot Hero mentality by being instead greatly charismatic, thoughtful and determined, even if lacking a lot of subtlety. Tokine, the Weak But Skilled foil to Yoshimori's Unskilled But Strong falls far from the Damsel In Distress, and more often than not actually saving Yoshi via critical thinking and careful planning. Even the minor characters have their own quirks and charisma that makes you root for them just as much.
The Kekkaishi all have one skill at their disposition: the ability to create a barrier and lock things inside, as well as destroying what is within. That is their only weapon (granted eventually it expands, but it's a minor point), but the brilliance lies on how the Kekkaishi are able to use the same skill creatively to deal with their opponents; from Yoshimori creating several consecutive barriers to increase the overall power and defense of them to Tokine creating thin but long piercing barriers that require little power but can keep the Youkai struggling to escape. The overall result is fights are no longer about abstract measurements of "I'm faster and stronger than you!" but instead become "what is the best way to trap him in my Kekkai?", making you not only understand but marvel at the character's ingenuity to defeat foes with something as simple as invisible shattering barriers.
I could go on about how the antagonists keep you thinking if they are really bad people, the complex Myth Arc that will keep you wondering about the true intentions of a number of characters and the careful explanations given to japanese folklore and culture, but you're better off reading the damn thing already.
Tallen M.F.~