I rewatched this recently, and it's better than its reputation. Michelle Gomez is incredibly giving a chaotic evil performance for the ages, her murder of Osgood is just cruel and evil. Peter Capaldi matches her every step of the way in a great performance where he's filled with horror and dread until his jubilant realization at the end. The climax of the 'soldier' story arc with the Doctor and Danny is thematically perfect. Finally, the heartbreaking ending paying off the Doctor's dislike of hugs with him and Clara both lying to make the other one feel happy, it's devastating and beautiful.

(Also the gag with Jenna Coleman's eyes in the opening rules)

(Oh, and the Doctor falling and making into the TARDIS is badass)