Although it is an anime where giant robots fight each other, the action is slow and usually won't last long. No epic fighting scenes here. What this anime is trying to do is to reveal several moral and ethical questions, and is more suited for people who like to think. People who like action series like Bleach or Naruto, probably won't like this very much. People who like shows like Serial Experiments Lain, will probably love this. It has a similar dark and depressing feel than Serial experiments Lain, actually.
This anime has one of the most well-thought plots i've seen. The story is original, and it works. I won't go deeper into this matter, because i'd hate to spoil it for someone.
The animation was pretty good at most parts, but sometimes (happened two or three times) a character moved inhumanly fast, but it shouldn't be anything to ruin your enoyability.
I didn't really pay too much attention to sound, and in my opinion it was just fine. Only flaw was that one of the characters voice was extremely annoying. Luckily that character didn't show up too frequently.
The characters was one part i liked alot. There were no "absolute good" characters, and they all seemed to have their own troubles.