I really enjoyed this series, because it was different, and it didn't take itself at all seriously, and thank goodness for it!
I also really liked that it is set in London, around the old areas of Spitalfields and the city - Jack the Ripper territory.
I enjoyed the look and feel of the locations, beautifully designed and detailed - especially the Stacks (the huge underground library of demon hunting lore). And while it moved a little too fast for me at times, I found it very entertaining nevetheless.
I'd like to see a second season (all those Buffy fanatics: remember how bad season one was by comparison to season 3) - there's so many places it could go.
If you haven't seen it, give it a go.