First of all, I'm a very biased reviewer since I've loved the show since its inception with the documentary "Ghost Adventures" that was aired in 2004. Zac, Nick, and Aaron have the three crucial elements that set their ghost investigative series above and beyond the rest: 1) compelling audio/video evidence, 2) entertaining, and 3) scary as hell! Other series like Ghost Hunters, Paranormal State, Ghost Stories, Celebrity Ghost Stories, etc. are okay, but they are missing one or more of the crucial elements listed above (some do great investigative work and have superb evidence, yet are neither entertaining nor scary...as a show on the paranormal should be).
One particular detail I really love about the show is that they replay audio/video phenomena 3 times, so you can hear or see what's going on when they capture evidence - whereas other shows only replay once, so you don't know exactly what you heard or saw. Another particular detail I like is the format; the boys go through the history of a haunted place for the 1st half of the show, then they do their creepy/chilling investigations for the 2nd half of the show (great to watch late at night with all the lights off on a surround speaker system).
One critique I agree with (in regards to some of the comments listed already) is that the seasons on disc don't correspond with the seasons on TV, which causes some confusion. The reasoning behind this, I think, is that consumers can get more episodes for their buck when they buy the DVDs (for example: season 2 only had 8 episodes on TV, while the DVD had 12+1 episodes [some from season 3 on TV]). I already bought all the seasons/episodes on iTunes, where the seasons (or volumes as listed on iTunes) match the TV seasons, so I already know the order they go in. I just want buy the DVDs when they come out, as well, so I can watch the shows on TV, because: A) larger screen/better resolution, B) better sound (unless your computer has expensive speakers), and C) better navigability than on a computer.