There's at least two seasons' worth of material crammed into this 3-parter, which creates a manic feel and leaves many side characters without development or closure. Claes Bang's Dracula is a highlight, as is Dolly Wells. But the story treats everyone else as disposable and the pacing is uneven. [Spoilers follow]
The first two episodes are the best, but so much of that development is undone by a terrible finale that introduces a whole new cast of characters that we're meant to care about without really justifying why. Lucy Westenra's character arc should have been epic, but is so rushed as to be confusing. She loved death? Would be great if you had shown us that. Instead she is portrayed as a shallow influencer marrying for money--which would seem the opposite of someone wanting to die. Key plot points--was Zoe's lab trying to weaponize Dracula?--are left dangling in the rush to the end. I was unsurprised to find out Sherlock's showrunners were behind this, as the finale was every bit as random and detached as that show's was.