Spiral: Suiri no Kizuna can be almost what you would call reading 15 volumes of bliss. The mix of excellent artwork, a mind-boggling storyline, fascinating characters and plot twists that you would not have expected all work towards creating the dictionary definition of an 'enjoyable read'.
Story
Spiral's storyline is one of the decisive elements that keep it apart from your usual run-of-the-mill manga. While it begins on a rather lackluster note, seemingly appearing to be a murder mystery, the plot quickly develops into one that leaves you with many questions asked, and begging for the answers to come quick. The mystery behind the existence of the 'Blade Children' is the most pivotal plot element, one that you'll only find out from reading this title.

Art
Obviously, if you ever notice the various pieces of Spiral artwork, you'll realise that this series has excellent artwork throughout the entire manga. While the art itself does develop as the series progresses (it appears to be cleaner if not even more super-deformed or 'shoujo-like' during later volumes) you'll most likely love it from the beginning to end. The existence of bishies and bishoujos are also rampant in Spiral, so you won't miss anything out in that department. Obviously if you're looking for a more realistic art style, Spiral may not deliver.

Character
Most likely Spiral's strongest point is it's wide variety of characters, many that you'll probably love rather then hate. Unlike many titles, who is good and evil is even more ambiguous in Spiral, there is no clearcut 'good' or 'bad'. Because of this, the protagonists and so-called antagonists are all individuals you may grow to love. Character development, especially for the protagonist, Ayumu, is something you will most likely look forward too. Besides that, most of the characters are both humorous yet attracting, you'll probably end up hoping they will all sincerely receive a happy ending.

Enjoyment
What can I say? Spiral was seemingly one of the most enjoying reads that I've ever laid eyes across on. The mysteries can be rather irritating at times, but you feel satisfied when you finally know the truth. The art is plain eye candy (which is a benefit I hope), and the characters are ones I think anyone can grow to love. After reading numerous titles, I can safely say that Spiral is able to tower above many of them. The mix of mystery, logical and physical (and violent) battles puts this series into being one that can be read by any type of person almost.

Overall

Summarising Spiral's strongest areas:

Excellent artwork for those who seek this type of eyecandy (that is, cute girls and boys that may not be on the realistic side).
A gripping story that keeps you on the edge of the seat for the entire time. Next to the mysteries, Spiral also brings in much comedy, action and even slight bits of romance.
Likeable characters you can grow to love.

It can be safely be said that Spiral is a series that deserves its 10 in this review. Spiral's mix of story, art, character and enjoyment is not something that can be easily overlooked. While they are various minor irritations one may find with this title, it can most likely go unnoticed as you stare in awe as the mysteries and events unfold in front of you.