Legendz is a pretty typical shōnen monster battling series. Instead of collecting all the monsters, characters generally have one specific to them. There isn't too much unique about the series, it tends to fall into all the established tropes of shōnen manga. The series is short however, as it only occupies four volumes. It might be enjoyable if you are looking for a short shōnen series.
The series establishes the main characters quickly, and all of them have an established back-story of how "Legendz" became a larger part of their life. This works doubly as it also establishes the numerous characters' relationships with their monsters. The
disappointing part of this is that secondary characters are introduced and dismissed so quickly because the series is so short. The first volume focuses about school-yard battling, and most of the characters are interesting. The secondary characters introduced after that story arc are all much more dull. The character development tapers off as well, as the series becomes more focused on bigger battles with more on the line. To develop tension, pages that could be used on back-story or universe building ends up wasted on lengthy battles that all end up blurring into each other.
The artwork in the series is decent, the characters presented all have a unique look, however the monster designs in the series are generally pretty bland. A lot of the detail that is present early on disappears as the series gets near the end. I'm assuming because the series got cut off, the creators had to slap an ending together without much time.
The fact that the series died out so quickly is perhaps the most disappointing part. Perhaps the art could have improved, or the story redeem itself, but since the series had to close so quickly, I suppose we'll never know. In the end it's an interesting--if bland--entry in its genre.