Moreish and very watchable. There are occasional holes plot wise, however in the main the series is very much worth spending time with.
Set in postwar London, Gatiss plays an eccentric book shop owner who moonlights as an ever so slightly Sherlock-ish sleuth. He has a 'letter from Churchill' which acts as his detecting credentials and gives him authority to be involved in some knotty crime solving shenanigans. There are lots of plot hooks and twists, and the main characters are all well formed. We discover lots of skeletons in cupboards and the stories behind them are unveiled at the perfect pace as the series glides stylishly along.
There's a wonderful look and feel to Bookish - it's very much a Mark Gatiss piece, but aided and abetted by the immersive and impressive production design. The resultant look and atmosphere (think League of Gentlemen, Sherlock, etc etc) along with the characterisations Gatiss conjures all help to elevate Bookish way above other recent TV detective/crime dramas.
Apparently a second series has already been commissioned - I think that's justified and something to look forward to.