I picked up Volume 1 at Kinokuniya for lack of anything better to do, and the synopsis sounded cute, if not particularly unique or interesting. Given the lack of expectations, it would've been hard to disappoint me, but Kage Tora somehow managed even that. To be fair, I'll note here that this comment is written with only the first volume in mind; I've only flipped through the 2nd and 3rd volumes before giving them up. If this manga improves drastically later, then I stand corrected.
The main characters of note are Kagetora, the ninja/martial arts instructor/bodyguard, and Yuki, the successor of the Toudou family. Kagetora's supposed to be one of the senior ninja of his clan, but nearly all his exaggerated attempts to save Yuki and help her around at school have failed. Miserably. There is no character depth, because he spends the entire volume blushing at the thought of Yuki and telling himself that it is not the ninja way. Yuki is a complete airhead placed there for fanservice. I find it hard to understand how someone can be that naive and dumb; very little thought actually passed through her head.
Plot... what plot? Kagetora's supposed to coach Yuki in martial arts, but she's clumsy and a complete ditz, so that goes nowhere. The entire story thus far is dedicated to Kagetora blushing and silently berating himself for falling in love with his master, and Yuki innocently clinging onto Kagetora with the mindless adoration of a puppy.
The art is nothing to write home about either; it's fairly typical. Not particularly good, not particularly bad, though Kagetora is definitely drawn better than Yuki. Yuki's facial proportions are occasionally a little off, so readers should prepare themselves if they're really picky about the art.
All in all, I'd say - pass, pass, pass! There are many better manga out there with more interesting characters, better plot, better art, and yes - better fanservice.