There are a few things that immediately grab your attention about this show. First, the start of the series is extremely fast. They put you in the place of the main character and you know everything he does... which amount to nothing. You sit there for a moment after the first episode wondering what the hell just happened. Second, you find out an extremely interesting looking world. Third, if you can keep up, you find a brilliant concept that continues to get more in depth and interesting as the series progresses.
As I said, this series starts with an extremely interesting premise and continues to add minute details that make it even more important. It draws the viewer into a promising world, and continues to raise the stakes as the series goes on. The only draw back is that it is easy for the story to go over your head if you don't pay enough attention.
This series does a great job with trippy animation for their alternate world. The character designs, by and large, are very original, the girls are SUPER cute, and the like. Unfortunately, the main character seems a little too normal. His character design stands out like a sore thumb compared to the others.
The voices themselves are well done, as are the OP and the ED, but I find the sound track somewhat lacking. It is by no means inadequate, but it is certainly nothing memerable.
Many of the characters are extrememly well done in this series. Many characters constantly surprise, in a good way.
Anyways, overall, it is definitely worth the watch. Some very interesting concepts get deeper and deeper and are surrounded by interesting characters.