I must be the only person who's glad Osgood's dead, never really cared that much for her, just some annoying geek to me. Plus her death had a nice dramatic impact, It showed what the Master is truly capable of.
Osgood as a companion would have been very interesting. What if a fan traveled in the TARDIS? Very similar to Izzy, but a decade older.
It's interesting. The critical acclaim for this episode was great but the fan reaction on the message boards I've visited is very mixed.
That's the way it's been all season. The reviews love it, the fan reaction in fora and social media is more ambivalent. It's very puzzling why opinions are as divergent as they are. In some cases, I've wondered if reviewers are watching a different show than I am. (I haven't hated this season. It's a very polished production. But I don't like thinking about it, because I stop enjoying it when I do.)
I think in many ways you've answered your own question. Fans have a tendency (me included) to think too much about the show rather than just enjoying it for what it is.
I have several friends who I wouldn't count as fans (as in the context of fan as someone who posts on here, watches a lot of Dr Who etc) who have been less than impressed at times this year.
I've enjoyed S8 overall, there's been some ropey episodes, but there always are. I like Capaldi and the season, as you say, has been very slick.
Have I felt the same unbridled joy I felt during most of Smith's run. No, I'm afraid I haven't, but doesn't mean I don't still enjoy the show, I just miss Matt, Karen and Arthur, but that's the nature of Doctor Who, and Capaldi is a perfectly good Doctor (aside from, as I said, he sometimes seems to fade into the background a little) and, for me at least, Moffat hasn't been in post too long (though with the best will in the world I think he ought to be making plans to move on soon, just from the perspective of giving the show a bit of a shakeup).