First off, I will begin by saying that this in not an anime everyone will find enjoyable. It is very similar to a long winded Baccano!, following many different stories, making it very hard to identify with a single character that has a lot of depth. Next, the way the story is presented, it makes the series seem episodic, following a new or at least a relatively unknown set of characters from one arc to the next, almost giving it the feel of a set of sequels from one arc to the next, often ending with a character being put aside and seemingly disregarded in term of the plot. This, however, is not the case. Each arc is actually quite important to the final ending, making the "side-stories" actually being integral facts and the disregarded characters being picked back up. This is not a series for people with short attention spans, people that don't pay close attention, or that need a single uniting thread to keep their attention throughout a long (27 episode) series. This being said, I'll attempt to review the series from here on out without any spoilers (which may be quite difficult for this series).
Story: For this series, as briefly mentioned above, there are a lot of subplots taking place throughout the first 20+ episodes of the series, taking up only a few episodes per subplot. This gives the series a feeling of just being a lot of filler when, in reality, very little of these stories are actually filler. It is most like each of these subplots are but a thread that, when put together, make a full rope of a plot, escalating at a rather well presented (albeit, cliche'd) end message and a finale that takes several unexpected turns. This being said, if you can get to the end of the series, the story is actually quite exceptional.
The presentation of the story itself is rather reminiscent of Baccano! or, in a more recent and slightly more accurate example, Durarara!, following different characters almost exclusively for a single arc, then putting them aside for a little, sometimes as long at 15 episodes or so. This makes the story seem more like a branch, spreading off into different directions, instead of a standard linear one. All the while, there are rather interesting and intricate subtleties being set into place in the background for the engrossed viewer. All these things, when culminated, add up to a good story that can't be appreciated until viewed in hind site.
Animation: The animation of this series is fairly strong, having only weaknesses in the slight failures at CG near the start of the series (which, to my recollection, only happen in the first few episodes) and the fact that a few of the characters have similar designs, making them easy to mistake for one another, even though all the other designs are rather impressive and easy to differentiate. Other than that, there are nice sceneries and backdrops and relatively few complaints to be made about the animation quality.
Sound: The OPs and EDs are fairly catchy, and the backdrop sounds were appropriate and occasionally impressive. Being a former jazz artist in high school, I really appreciated the jazz they threw in here and there, keeping the OST fairly balanced with different sounds.
Characters: How you view the characters is very important for this story, but also it is very easy to dislike them. A great many of the characters have their own arcs, giving many of them characterization. However, they are then pushed aside or killed in some cases, kind of making you hate whomever wrote the story while you are watching it. However, there are so many interesting characters with some depth that I think it prevents your anger after the first few arcs. Another complaint is that there are a lot of cool characters that have no depth whatsoever, or that you don't even learn what their power is. This, however, is unavoidable because there are simply too many characters to do so, and can be forgiven.
Overall: About 20 episodes into this series I wasn't expecting anything I could give above a 6/10 or so. A few fun characters, a few good action scenes, and not much else. However, after seeing it all come together, I have another opinion of this series. Although a few of the twists that happened about 3/4 of the way through the series were kind of foreseen, the last few episodes kept me guessing, not knowing what to expect and not expecting things to crop back up again that already seemed to be put to rest. If I had to compare this series to others, I would have to say it is like a 26 episode Baccano! or the first half of Durarara!, with Lelouch and Suzaku from Code Geass, Yukito from Air, and a climax similar to Shakugan no Shana. The first portion of this series is kind of hard to sit through because it seems like a hero of the week theme, but it ends up working in the end.