Warning: Spoilers Ahead
I wasn't sure what to expect when I started watching this. I was definitely expecting action based on the summary of the show and a cool plot. What I got was that and much more. The story is centered on an assassin who works for an organization trying to bring world peace called Chronos. The catch is that they aim to do so by killing people they deem evil. The main character, Train Heartnet, is their best killer, trained since he was a kid, and is known as Black Cat, an assassin who never failed his missions. Train's life changes when he meets a girl named Saya who sets him on his path to freedom and redemption. Meanwhile a sweeper named Sven and a thief named Rinslet Walker collaborate to rescue a girl who was made from nanotechnology from the hands of evil. Train is ordered to kill that same girl, and so their stories intertwine and insanity begins.
Story: The story was pretty interesting and held my attention. There are several plot twists that keep you on your feet, and generally it kept you wanting more. There are a few episodes where the plot wasn't too interesting though and which dragged, but only a few. Also, the last four episodes, while serving as pretty good finale episodes, felt a bit rushed. The last episode especially was extremely rushed. It could have easily been stretched into three episodes or so. The ending itself I loved, but the episode as a whole could have used some fixing.
Overall the story was well-crafted though, with small seemingly unimportant details mentioned in the first few episodes become relevant and very important in the end, which is somethingI absolutely love as it shows hood planning and makes your jaw drop.
Characters: This is where the show shines very often. Train is extremely well-developed, easily the deepest in the cast. We slowly learn more about his past as the story goes on, and his path to redemption as well as his motivations are fleshed out excellently. Eve, the nanotechnology girl, also has excellent character development as she learns that she has freewill. Her situation is very similar to Train's, and an excellent parallel is drawn between them. Then you have the lovable Sven, a gentlemen with his crazy suitcase and vision eye. Rinslet is fun to watch as well. Creed was a wonderful villain whose obsession with Train did much to add to his creepiness. Sephira of Chronos was awesome as well. The character dynamics were interesting and a pleasure to watch, especially the touching bond between Eve and Sven.
Of course, Saya deserves a special mention on her own, because her story was easily one of the most brilliant aspects of the show. The way her death motivated Train as well as her everlasting influence on him was shown again and again in all of Train's later actions, and its no exaggeration to say that the whole show is built on her character.
My only complaints here is that some villains, like the Apostles gunman and the gravity guy, got almost no development before they were killed off, and several Chronos characters suffered from this as well. Also, Train's transition into a more easygoing person, despite making sense, was done a bit too abruptly and should've been done more gradually.
Music: Nothing to say except it's amazing. Loved it, really set the mood.
Animation: Generally pretty good, became pretty amazing during the fight sequences. At times though it was a little odd and had a few awkward moments and at times the coloring in the scenes was a bit strange and too stylistic, but overall the series is nice to look at.
Action: Pretty awesome when it came. The animation was usually nice and fluid and the action scenes were often incredible. They did get a bit less impressive near the end, but overall were very good.
So, overall the show was awesome, I find myself rewatching parts of it. If I was writing a review for the first seven episodes, which were nearly flawless, I'd probably give it over a 9. However, it did stumble a little later, despite remaining very entertaining. I enjoyed the moral dillemas presented in it as well as the recurring themes of freedom and redemption. The characters were generally fantastic. I'm not giving it a full score due to a few issues, such as its sometimes rushed pace as well as the rushed ending, as well as Train's abrupt transition and a few episodes that dragged, but despite these flaws it remained an ex cellent watch and I definitely recommend it to anyone looking for a good action anime, better than most out there. I know it's a series I'll keep coming back to to enjoy again.