This is a piece of brilliance. There has been so much thought gone into this series and it clearly shows. The physiological side of the anime is incredibly intriguing and thought provoking. The characters are written extremely well and realistically. The plot from the very start is awesome as well. It gets straight into the story. This is an ABSOLUTE must watch.
If I am being critical the only negative, and I use the word extremely loosely, is the length of the series. 74 episodes is a lot of anime to watch.
I am giving this a 10/10 and recommend that you watch it.