I didn't so much mind the Torchwood characters being flawed and, well, not getting on so much. I think you put the finger on the sex problem though - all too often the plot seemed to stop with a "hey! look! sex!" moment rather than the sex seeming to arise naturally from the story - though it wouldn't surprise me, if I went back an did a rewatch to discover that there was less sex than I think, part of the problem was the way it often seemed to be sign-posted in an "ooh! aren't we being adult" kind of a way.