Kill the titular character once and it's genius, trying again a mere 7 episodes later you kind of lose some of the charm and shock. It's not that it wasn't effective for tension and or drama, it just created less this time round. Also, now that I think about it, they did it in The Big Bang as well.
While I still throughly enjoyed the episode, Rory and Amy creating a crop circle message with a Min Cooper was a stroke of brilliance, I felt the episode lacked some decisiveness and or clarity regarding River.
While this is not a huge flaw, the fact that Moffat squeezed in River growing up with Amy and Rory through their childhood, cemented their "courtship", a regeneration, her revelation of what River Song meant to the Doctor, her entry into a career in archaeology andher turn 360 from heroin to villain back to heroin was simply put, a little jarring.
The real clincher as to weather you'll love this episode or become frustrated, depends on if you see this pacing as dense or rushed. I'm personally on the fence, I really wanted flashbacks to Amy and Rory as children and teenagers that weren't preoccupied with establishing Mel. Because the scene were Amy confesses that she thought Rory was gay was my favourite scene. Not only was it funny and sweet, but it was the exact moment when they realised they more than just liked each other.
I should really point out some stuff I loved, I've been harking on about the down sides of the pacing for too long already.
The entire cast were at the top of their game and this seems like the first romping adventure Moffat has done since The Eleventh Hour, even the extremely fun series' opener had very dark under tones throughout.
The antagonists here where interesting, I'm sure they'll come up again. Mind you they weren't the villains that the marketing made them out to be, nor did this have any intention utilising Hitler in any real way. All a smoke screen that was intended to hide the true story that was sneakily presented. I didn't honestly mind all that much, we've visited historical figures before and with Nixon already filling that requirement this season, it wasn't all that bad making him the bait and switch.
I'm have to say, I've thought to myself that the odd episode could've been made into a 2 parter, here it really should've been more so than ever before, but I digress. A ridiculously fun, if busy episode that has so much going for it, that I'm flabbergasted how they'll top it in the finale.
EDIT: Forgot to say that the episode flew by in no time, I've seen 20 minute comedies that have felt longer.