I thought that Torchwood season one was generally bad, and that season two was downright terrible, but I've stuck with the series because it has potential. I felt that if the writers would only recognize the strengths of the premise -- and brutally stomp out all of the self-introduced weaknesses -- they'd end up with something truly great.
Usually my prayers go unanswered, but season three of Torchwood is absolutely amazing. They've darkened the tone, chucked the juvenile sexuality, trimmed off the extraneous character complications, and written within the budget. It is five episodes of perfectly-maintained suspense, anxiety, and outright horror. The aliens -- known as the "456" -- are the most terrifying creatures I've seen since...well, Alien.
In true Russell T. Davies style, however, the focus of the show -- and the REAL monsters -- are the buerocrats and functionaries who serve to represent humanity at its worst. It's bad enough that the 456 exist...what makes it TRULY bad are the petty foibles of those we expect to protect us.
If you've never watched Torchwood, go out and rent season three. Skip seasons one and two entirely; don't worry, you'll catch on quick enough. You might squirm when John Barrowman does his obligatory crying, but this time around it's kept to a tolerable level, and he really DOES have something to cry about.
PS: Actually this was very similar in tone and theme to a 1998 British mini-series called "Invasion: Earth." You might even accuse Davies of (perhaps unconsciously) copying it. Still, the particulars are different enough to make both series' distinct AND worth watching.