If you are wondering about the 6 discs/4 discs comments, it is due to the fact that the DVD series comes with 6 discs and the Blu-ray series comes with 4 discs. Same total number of episodes.
Very entertaining. True to its name it does stay on the fringes of science. Every single episode will hold your interest. Most episodes would work as stand alone s, yet each one advances the general thrust of the series as well; adding crucial elements to the overall jigsaw. The acting is really good. The plots are great. It could easily hold its own against the more somber, darker X-files or Supernatural. Each and every season is worth the long wait!