Amazing.
Wow. That was the best episode in years, possibly since The Waters of Mars. I just don't even know how to process all of these emotions. I've always been a Whithouse fan, but this was just so far beyond his previous efforts. The first one that really felt like "From the Creator of Being Human".
The emotional drama, the maturity, the themes, everything was top notch. Jex was a wonderful and complex character both as a villain (but not really) and foil to the Doctor, and the Gunslinger was so good. I loved how both of them evolved over the episode. Isac also gave a great presence in his leadership and death, and evoking the themes of mercy. Seeing this follow on right from last week makes perfect sense (and I'm now completely happy with how Dinosaurs on a Spaceship ended). The Doctor goes through great turmoil and growth, and even Amy was bearable here.
Just incredible. A true tour de force.