See, season 1 of Torchwood was a bit of a disappointment (though the last 5 mins of the show made up for every single let down). It is the show that was birthed with a silver spoon in its mouth, as a spin-off of Doctor Who there was no way that it wouldn't do good, but I was consistently let down by the series So much damn frustration. It has moments of brilliance only to be shot down by chunky writing. however, I am willing to forget and forgive as producers, writer and even the creator itself has admitted to the mistakes they made last season and have gone about correcting it. From what I have seen of this season they have indeed corrected all the things that was wrong with the series.

So, um, in conclusion, if you wish to watch s2 it is probably not a bad idea to watch s1 of Torchwood, and definitely catch up on all the episode of Doctor Who that Jack was part of. Jack Harkness' character makes so much more sense if you know what he was/is like with the Doctor.