Given a few years, all those bad reviews will look exactly as they are - a kneejerk reaction to this not being identical to the first series.
I'm enjoying it, too. It's not quite as gripping as the first series, and it doesn't feel like there's quite as much depth (maybe because we've got half a dozen stories, rather than the three or so we had in the first?), but it's still good television, and I'm glad it's not a rehash.
I agree with that Vaughan's performance is good. However, my pick has to be Colin Farrell. Kitsch isn't doing anything for me, McAdams is putting in a solid performance, and it's great to see this other side of Vaughan, but it's Farrell who's really knocking my socks off.