Note that these are my thoughts on season five itself since I've already seen it. The DVD has not been released at the time of this writing, so I can't comment on the DVD extras.
Although I thought Season 4 was a bit rough (understandably, considering it was a character transition period), Season 5 definitely more than makes up for it.
Season five of Being Human recaptures the wonderful balance of humor and drama of season one, with a slight difference-- while Mitchell, George, and Annie seemed to have their own separate storylines that eventually meshed together, Hal, Tom, and Alex's stories are more intertwined from the start. This seems trivial until you see how close friends Hal, Tom, and Alex are in comparison with Mitchell, George, and Annie. Both groups are friends living together, but new trio seem inseparable compared to the original. They're all in it together-- Hal and his struggle with bloodlust and readjusting after 55 years of isolation from the outside world, Tom by his side also trying to live a 'normal' life having been raised as a nomadic, vampire-hunting werewolf, and Alex, who is still trying to come to grips with life as a ghost after her death (which Hal is tangentially related to). In spite of each character's unique condition, their day-to-day struggles still seem familiar with our own.
This season is the first and, unfortunately, only season in which we see these three characters together on their own, with no 'baggage' (characters from episodes before and during the cast transition). It's a pity the show was axed to make room for other experimental shows on BBC 3, since the chemistry between the new trio is phenomenal and they still have a lot of potential with their stories. Though Hal, Tom, and to an extent, Alex's characters have already been established in the previous season, they're given more depth through backstories. You're shown glimpses of their former lives, who they used to be, and how far they've come. Even the secondary characters are very well developed in the episode(s) they're in.
The season arc is enjoyable and the overall pacing of this season is much better compared to season 3 or season 4. The finale is excellent, heartbreaking, and somewhat controversial.
To those who haven't gone past season 3 because of the character change, you owe it to yourselves to make it through season 4 (for background understanding) so you can watch this season. Sure, Mitchell is still missed, but Damien Molony does a fantastic job at playing Hal, whose personality is very different from Mitchell's-- it's clear that the writers did not want a Mitchell 2.0. Once you realize Tom isn't as naive as he appears, you also see that he's incredibly loyal and selfless. He's the heart of the group. Alex is, well, the soul of the group. Her fiery, snarky attitude is almost reminiscent of Amy Pond or Donna Noble from Doctor Who. She has a very active personality, which serves as one of the catalysts for the overall season arc. Hal and Tom's bromance easily rivals George and Mitchell's.
To those who aren't familiar with this show, or have only seen the Syfy remake-- consider giving this a shot. Each season ranges from 6-8 episodes, which means the plot is more condensed than what you'd expect with US shows, so things get a lot darker a lot faster (especially during the 3rd season). It's far more character-driven than the North American version.
Most TV shows tend to overstay their welcome and become stagnant. Cast changes are not usually handled very well. Being Human Season Five demonstrates that this show still has so much life left in it and is an excellent example on how to have an entire cast overhaul without destroying the heart of the show. It's a season (and show) well worth watching.