If you liked the books and are fans of the kind of british humour that makes Terry Pratchett's work so wonderful, this will disappoint if not anger you. I'd recommend the Frankenstein chronicles or Carnival Row if you want a gritty or high fantasy detective series that has well developed characters. The Watch is more of a crime series based in the discworld with the characters sharing the same names of the characters in the book. Without the same characters it just doesn't have the magic, the stories (mysteries) can change but that only works when you have the fully fledged characters that Terry Pratchett brought to life.
Every bit that made the watch funny or endearing has been sucked out. Its like the person that wrote this adaptation hasn't read the source material and if they had they didn't get why this as popular. So it just has a film noir/ punk vibe that makes me feel like they loved the video 'smack my b*#@h up' by the prodigy. It is devoid of character and parrots pratchett in all the wrong ways. The writer just didn't get what made the night watchmen great.
It is as if you have ordered a deconstructed burger in a swanky restaurant, expecting the key components to be present on the plate if not all together in a way you know. But this is not the case, instead you are then guided by the miserly waiter through the kitchens, out the back, onto the number 32 bus and then get off after 30 minutes and 4 pounds £ lighter, and then the waiter stands and points at a cow grazing in a field. He hands you a fork and says 'I'm just glad we stopped doing reconstituted meals'.