Well, someone has to be a party pooper from time to time, so let it be me this time.
I cut short my viewing of a reasonably interesting Titanic documentary to watch Sherlock, and my expectations were high. While I admit that it was a fairly enjoyable 90 minutes of drama, I thought that this was probably the worst Sherlock yet. The actual story veered between the utterly unbelievable to the pointless. The dead boy in the car was a total red herring - why bother? - and, like others here, I find Mary a strangely unengaging character, believable neither as a super-soldier nor as wife to John.
On top of all that, the trailers had been completely misleading (and not just clever misdirection, which I could forgive!). Toby Jones' character had been thrust front and centre in the trailers, and if I'm not mistaken, we got a half-second glimpse of him on a poster at a bus stop, and that was it. I can only assume (hope?) that the 3 stories in this series are linked, which will bring Mr Jones and the bus-girl into the story.
So, as a stand-alone tale (forgetting that it's Sherlock), I'd give it 7/10, and most of that is for Mycroft.
If it is indeed part one of 3 of a larger tale, then I'll cheerfully eat my words if it improves, but as a Shelock Holmes mystery, it's only a 4/10 from me.