Wormhole summed it up - Moffat's just not trying anymore. Personally, I think between the Trilogy of the Doctor and picking the New Doctor, he was spent. The last two series have been lucklustre in their own ways:
Series 8 had an OK arc with a disappointing conclusion and a great number of forgettable, uninteresting episodes or near-great episodes with terrible conclusions (like, Listen, which is fine until we get Moffat shoehorning the barn from Day into the First Doctor's timeline, basically retconning his invention to a fundamental scenery for the Doctor, not to mention having Clara influence his thinking for the past 50 years, too - ugh!), resulting in a disappointing eighth series.
Series 9 had a good deal of two-parters, but without a lot of interesting moral issues or characterization (even the opening two-parter with Davros is sorely lacking in engaging dialogue between the Doctor and Davros, making for a disappointing clash of characters overall). Add to that an absolutely non-sensical story arc that is beyond stupid (what the hell is the Hybrid anyway? is that threat gone?) and the most boring side-character of NuWho in Whats Her Name (aka Me).
So, for me, I enjoy the character moments greatly in series 9, but they're not enough to go back to that series. The story arc is awful, and the last episode is beyond excrutianting to watch (just let Clara die already!). And its just so clear to me that Moffat has nothing left to say anymore, that I worry series 10 might be even worse than 8 and 9. He's bereft of inspiration, as he clearly told everything he could have by Time of the Doctor. I really wish Chibnail had come to the show with series 10, personally.
In any case, at least Capaldi was consistently entertaining, trying to act old in an old man's body, before actually becoming an old man acting out deceptively senile but still doing better of them all. Brilliant.