Phantom: Requiem for the Phantom is a high profile and well presented series with an interesting premise - that a criminal organization programs people to become hardened assassins. However from the first episode and until the very end it presents an extremely weak storyline, episode one presents a man with amnesia (that laziest of plot devices) who has been selected to survive some "training" with a veteran assassin and Navy SEAL. The man directing the training (Scythe Master) does nothing more than throw the protagonist (Zwei) into the deep end, Scythe doing nothing more than spouting vague and weakly whimsy statements. This is a big problem that reoccurs throughout the series, that Scythe seemingly does nothing but somehow magically churns out assassins.
As the story progresses we get several timeskips (another bad plot device) and vague circumstances which allow for storyline padding and filler. It's frustrating to see characters suddenly switch personality purely because there has been a timeskip, particularly when characters seem to act in entire contradiction to their formerly established personalities. Without wanting to give too much away the story is very linear, shallow and predictable; characters are bland, one-dimensional and schizophrenic.
The artwork for the series is almost uniformly outstanding. Aside from some occasionally bad CG, this is one of the best looking anime series I've seen to date - characters move with incredible smoothness and detail, backgrounds are usually quite beautiful. I cannot emphasize just how good this anime looks.
If anything the artwork is what offers the series some salvation, since the gunfights are so well animated and fun to watch. If you can sit through a bad storyline, watch the series for this alone.
The English dubtrack for the series was unusually good, one of the best I've heard in a long time. Despite the ridiculous lines the actors were forced to read, they did an excellent job delivering them; almost all the actors seem to fit the roles perfectly, and considering the (mostly) American setting this is the more fitting the audio track to listen to. Kudos to Funimation and their team for doing such a good job.
Overall it's a very disappointing series let down by a poor script, but one of the most visually interesting series you'll ever see. Such is the weakness of the story that I can't really recommend this series, but instead encourage people to check out superior programmes such as Black Lagoon or Jormungand.