Basically, it's the eyebrows.

While I appreciate the show devoting time to develop Clara's character, it was nice to have an episode that lets the Doctor be the Doctor. "Time Heist" really showcased the Doctors egotism when solving problems. It really felt like he was in charge, whether you like it or not. It's an authority that the character has been lacking since 2005. My favorite part about Capaldi's interpretation is the little bits of past Doctors that shine through. He makes it believable that this Doctor came straight from the 11th's cold detachment. While "Time Heist" is on the surface part heist pastiche/part economic satire, the real gems of the piece are the thematic callbacks to past episodes, particularly "The Rebel Flesh/The Almost People" (2011) and "Hide" (2013). This really makes it believable that the 12th Doctor is traveling in a universe that's still affected by the thematic consequences of his previous incarnation. It's almost halfway through the season and Capaldi is showing no signs of slowing.