The character screwed over the most by the book-to-screen transition and pov lost is undoubtedly Ned.

YES. It was frustrating to see him come off as totally ineffectual and kind of stupid on the show, because Ned may have been several things but he WASN'T stupid.

I kind of miss her killing the stable boy deliberately, rather than accidentally

I imagine they probably thought that a deliberate killing would make Arya less sympathetic, especially since all her inner thoughts are lost on the show.

So far most (though definitely not all) character/plot changes have worked for me, but I wonder if that may be because I didn't remember the book all that well.

I wish I were much further along with my rereading so I could have enjoyed your post even more.