I think the consensus seems to be that they should have repeated series 1 or run this one as a stand alone series, there were too many links back to make it straightforward, the beeb really missed a trick there. I seem to remember more shadowy background figures in series 1 - and I do remember Steve being horribly tortured ( couldn't watch) and some obnoxious kid on a bike running errands ( for Tommy?)- I really enjoyed this series, the combination of Keeley Hawes, ( not killed off but may be useful in series 3?), Vicky Mc Clure and Martin Compston was brilliant, they are all really good actors.
The ending was, as others have said, very rushed really, like so many of these series they 'draw out' - Salamander, Homeland were such examples, I guess we are expecting a killer ending so that whatever happens is a bit of an anticlimax, with the writers and production teams keeping their eye out for another series to follow on, so a more dramatic, final ending will never happen as they need to keep all the protagonists live and kicking for the next series!
Still, Dot gets promoted and made a permanent member of the team, so the corruption will perpetuate, and we may find out who is behind everything in the next series........................