This show is a classic case of: Good Idea, Bad Execution
It starts off simply enough with an intriguing (if all-too-common) storyline and interesting, shadowy characters. The first few episodes are pretty strong, focusing mainly on the development of the main protagonist and his interactions with his new employers and colleagues. I was eager to find out what would happen next, and in my eagerness, I ignored all the signs of what would come.
Very quickly the story takes a very cliched turn, and the characters become little more than billboards of irrationality. The motivations of the protagonists, antagonists, and pretty much everyone in the show, suddenly become contradictory to their earlier actions, thoughts, and reactions. The plot develops, rather quickly, from a biting psychological-thriller, into a predictable and unrealistic drama.
Not to spoil anything, but the hardened and brutal criminals of the first few episodes suddenly become weak and ineffectual, the anonymous, silent killers suddenly become flashy and all-too-eager to shout their names and identities from the rooftops. And of course, the calculating villains seem utterly incapable of understanding even the simplest of human motivations. It becomes all too easy to predict what will happen by simply having watched a multitude of bad television and feature films. If it's a cliche, it's probably used. If it makes little sense considering the setting, it probably occurs. Some people may think I'm being too harsh here, but the unrealized potential of the story makes the decisions of the writers and directors all the more questionable.
As the story begins to reach it's climax, one is forced to question the relevance of some major characters and earlier plot-developments. Little attention is payed to developing the rationale behind the decisions that the characters make; villain and "hero" (there are no real heroes here) alike simply act so that the plot can be advanced. Unfortunately, the plot advances in the least interesting and most predictable ways, and is itself full of holes. For example, a time-skip of two years leaves us with some people who look like they've not grown either physically or emotionally, and other characters who don't even closely resemble their earlier selves.
The result of the bad decisions made by the writing and directing teams is that some viewers lose interest in the outcome of the story, or the fate of the characters. Indeed, it is difficult in some ways to find the energy to care about the development of the plot and characters, when 90% of the time, your first guess is the right one. Actions are taken that seem to have no inner meaning or relevance to the actual story. Motivations which seemed ludicrous are revealed to be just that: ludicrous. Any hints that this may all be the design of some mastermind are left forgotten and we come to find out that the villains and "heroes" are all just that dumb.
To be honest, I find it difficult to rate this series as anything above mediocre. The art and music are all perfectly fine, though one particular theme is overplayed. The story is intriguing, if one is not looking for complexity or depth, and is not expecting something "new" or very creative. The characters are often interesting on the surface, but upon closer inspection, they become one-dimensional and sometimes, very contradictory. The drama is contrived and the plot-holes begin to weigh down any emotional value the events may be trying to convey. The ending was, in my opinion, fitting for such a series: cliche and not very well-executed. What started off great was, sadly, doomed to failure.
Overall, I give it a 5/10. In some ways this is too harsh, but in others it is far too lenient. Stories that don't take risks are usually boring and not enjoyable, but stories that take risks have to deliver. In my humble opinion, Phantom: Requiem for the Phantom took plenty of risks, but almost none of them payed off in the end. The higher one flies, the harder one falls.
In closing, I will put a quote from my brother about the show that I think summarizes it perfectly:
"It was like someone wanted to make a hard, biting, psychological show about assassins, but wanted to make it for an audience of fifteen year old girls."
((((After Edit: Upon further reflection, I have decided that this is perhaps the worst anime ever made, and have appropriately given it a 1 score. I have left the original review intact however.))))