Well, apparently he only drove because Martin can't, so I think it's realistic to be surprised by it. In the casebook, John describes it as the scariest trip of his life, though Sherlock seems a very calm and capable driver when we see him.

Mum doesn't enjoy it as much as Elementary I don't think, because she doesn't like Sherlock himself. She thinks he's a jerk, which he is, and so she can't get behind him as the hero as much. Whereas Miller!Holmes is really rather a sweetie underneath it all. Cumberbatch!Holmes is merely slightly less of a complete jerk underneath it all. I do wonder if we did it the other way around if she'd like it more, where she'd have had nothing to contrast it to. She's also never read any of the stories, so she misses some of the little references that make watching a lot of fun.