Cersei finally being Cersei
Though Cersei Lannister was fine with just using strategic dickery, passive-aggressive murdering, and weird double entendres to get her way through past seasons, her true nature came out this season. With Zombie Mountain acting as her id -- the physical manifestation of her pent-up anger -- and Qyburn, aka Gargamel from The Smurfs, acting as her eyes in the field and keeper of the wildfire, she finally stopped hiding behind proper royal channels and turned into the truly spiteful, incestuous, pretty person she's always wanted to be.
I honestly don't know what was more refreshing: her crushing glasses of wine in her Michael Jackson-in-"Thriller" Queen outfit, gleeful that she was about to blow up lots of people she hated and finally get revenge on the mean nun from Sister Act; or the look on her face as she says, "I choose violence" right before Zombie Mountain turns a member of the Faith Militant into a human "No Trespassing" sign.
Arya with the good name
So much of Arya's time has been in the service of one person or group. Tywin Lannister, the Night's Watch recruits, the Brotherhood, the Hound (which was admittedly great), and finally, the assassin commune/funeral parlor known as the Faceless Men. At first, Arya's involvement with the Faceless Men seemed exciting -- she's learning to be an assassin! She can put on other people's faces! She's studying the ins and outs of cleaning a dead body and mopping! -- but the goodwill I usually dole out for Mr. Miyagi-style assassin-training montage scenes quickly dried up once things dragged on and we had to deal with the humorless Waif, easily the worst character on a major television series since The O.C.'s Oliver Trask.
Perhaps sensing that collective anguish, the show finally put the Faceless Men plotline to bed, killing off the Waif in the process (pro tip: don’t attack a formerly blind assassin-in-training in the dark), providing Arya with a face-gift to Jaqen H'ghar and letting her get on with the business of going around the world killing people as Arya Stark, but now with the face-shifting skill set of the Faceless Men. The fact that she kicks this off with the time-tested Titus Andronicus callback move of human-pie-eating to extinguish Walder Frey is just the icing on a pie made from Freys.