I wouldn't say it is the best show of spring and that it might be the best show of summer either. I haven't seen a summer show yet and there hasn't been enough episodes of a summer show to gauge how good this can be next to any of them.
I like this show though. It didn't capture me right away. It took about 4 episodes for me to gain an interest, but somewhere around 5 or 6 to really get into it. It is definitely one of the more interesting spring anime and a bit complex, but I'm glad that I decided to take a chance on it.