I do have sympathy with the argument that Steven Moffat should've bowed out with Matt Smith after the 50th, but it could be argued that the 2014/15 series represented something of a second wind after an uneven 6 & 7, with some solid episodes amongst their number & Capaldi's stonking performance being the one constant throughout. However series 10 has been a real mixed bag in terms of quality, with even Capaldi not able to carry some of the material to greatness.
I mean it hasn't been terrible, but it's just been incredibly uneven & mediocre, & because of the producers inability to get a full series out in 2016, momentum for the show stalled & there was much more riding on this one being universally good, & it just wasn't. If these episodes had aired last Autumn, I'd probably be much more forgiving, but given how late they started production, that wasn't ever going to happen.
Not only that but you had Peter announcing his departure a full three months before any episode had even aired, managing to kill any remaining enthusiasm I had going into this series. Of course It's nice that he actually got a 3rd series to wrap his era up (as opposed to Colin Baker) but it would've been even nicer if his last run of episodes didn't feel like one long, glorified hold over, only really there to keep the show ticking over before Chris Chibnall takes the reins next year.
I feel like Moffat mentally checked out of Doctor Who a couple years back, & this one was him doing it purely for the paycheck, & that's not what the show or Peter for his swansong, needed right now.