I did wonder about Cersei's protest at his decision (that part of the book is hazy to me). I wonder if she really meant it, as per Varys' assessment that Ned is more useful to her alive.

I'm pretty sure it's made explicitly clear in the book that she didn't want him executed. Iirc, she tells Tyrion as much, and she has no reason to lie to him.

I actually rather like Theon in the show. Didn't care for him much in the books, but the actor pretty much sold the character to me. I love his facial expressions.