I've watched a bit of Torchwood before and while it's not bad entertainment and a bit hokey, never taken it seriously.
So, series 3, Children of Earth was something of a revelation. It's rare for TV (and especially the BBC) to use science fiction to reflect society, to ask difficult moral questions. But Torchwood: Children of Earth did this rather spectacularly. It also did sci-fi without resorting to huge levels of special effects, but instead by making a compelling drama, by learning from what people like Hitchcock knew: sometimes, it's about what you don't show that scares more than what you do.
To be honest, it's about the most shocking, serious drama that I can remember the BBC doing for a very long time. You've got to go back to something like Edge of Darkness to find something close to it. Seriously... it's Monty Python good, Fawlty Towers good. You just don't get TV this good and this mature in the UK very often.