I used to worship this show. Season one? As someone who loves 19th century literature, Sherlock Holmes in particular, I'm finding it hard to comprehend the season four finale. Don't get me wrong; season one and two were good. I loved the cases, the way they humanised John and Sherlock in a way lots of adaptations seem to forget to do. Season three went a little off the rails but it was alright because there was character development and something that seemed to be leading into a decisive, interesting plot. But no. Season four was one of the worst things I've ever seen. There were continuity errors, plot holes and even instances where cameras were visible in shots. The final episode was almost too bad for me to watch, I couldn't believe what I was seeing. A grenade on a drone? It all seemed like a joke. In retrospect, the show was nothing more than a clever crime drama with some fancy camera-work. It's constant use of gay people as punchlines (ie; queerbaiting) only got worse as the series progressed, not to mention the fact that almost all of the villains were queercoded, something I thought we'd left in the 90s.

TL;DR: Don't waste your time. There are plenty of better adaptations out there.