First half is brilliant enough even those who did not watch the tv series before can understand. But second half you need to have some background before. And the frequent time traveling made that worse. Is that because both are working on Doctor Who too much?
Is that the first time to formally incorporate the actual scene of the original story even the story line has been tuned? Is Mary also hired by Mycroft or just imagination? Is the line of Moriarty finally ended? Sherlock really wants his brother to die faster while his mind is attracted to Irene. He thinks Hooper wants to show something to him. Using Christmas special to explain Sherlock back from exile earlier can make Series four a reboot.
Make up of Mycroft is funny. First part of additional footage is nice but later part, just like the special, becomes boring.