Torchwood is Angel to Doctor Who's Buffy. Grittier (though Angel eventually departed from its darker tone) and aimed at a more mature - or at least older - audience. And like Angel's second episode, "Lonely Hearts", and following the violence and language last week, to demonstrate this difference "Day One" was, to use a phrase that might be found on the covers of certain video tapes, mainly concerned with sex. We got some fairly explicit TV-coupling, on-screen orgasms (lending new meaning to the phrase "going out with a bang"), voyeurism, masturbation and a dollop of girl-on-girl action (the first in the Russell T Davies Whoverse I believe). Not to mention the thematic interplay between physical intercourse and emotional isolation, another point in common with "Lonely Hearts".
But while the plot concerned the sex-driven alien in the body of the young Caryn, and while our viewpoint character was again Gwen, the story was actually about Captain Jack. A mystery even to his team mates, a man with cut off from humanity (and a no-doubt-to-be-revealed obsession with a cut off hand), someone with an intense need to reconnect with others, though he may not admit it, perhaps even to himself. "Day One" planted the seeds of a Gwen/Jack relationship, though I didn't expect it to develop to kissage so soon, even the relatively chaste peck we got.
On a related theme, it appears another series (season?) long arc will deal with Gwen's own ability to stay connected with her former life: her police workmates, her boyfriend, probably her family given Davies' pattern of introducing family members of the star's companions.
The supporting cast has yet to be developed beyond some rudimentary characterisation, though I'm sure they'll each get their spot in the sun eventually.
Plotting-wise, Davies again introduced a gimmick early in the episode to make one point, then brought it back to figure in a twist at during the climax. Last week it was the distortion field, this week the containment field. He obviously learned the lesson of Chekhov's gun on the wall.
Cardiff ("why always Cardiff?" as a friend asked) continues to provide some interesting overhead angles (show off that helicopter budget!) and the preponderance of Welsh accents are a point of difference.
PS: I thought the names for the first two episodes were incongruous. "Day One" sounds like a better name for a pilot, and "Everything Changes" implies a story in progress. Of course, the names make sense within their context, but it still threw me a little.