It had a great start, perhaps to some extent a good flow, they ruined it, the last episode made absolutely no sense, the filler episode which takes them back to the 20th century was indicative of the desperation to stay relevant. The part about eurus is just not planned well at all, Mary's role in the series was short lived, distorted and crappy, it was third rate at the best I'll say. However there are some good episodes like a study in pink, the blind banker, a scandal in belgravia, the reichenbach falls and his last vow. Apart from that everything else was a disaster and unnecessary, i am disappointed with the conclusion because this this is not what i expected of the series from watching the commencement. I'd say that even if you want to watch it, stay away from the last episode, it's toxic and so disappointing, especially if u watch all the four series in one go