The kid just ruins it. Simple as that.
The grand crown and strong point in this movie was the love story.
Somehow seeing the world in their hands already in ther other films just made a bit more sense than trying to buy how they pulled it off to make that happen in this film.
Lack of action and slow pace, BUT, if you like sentiment and emotion give it a go.
Sherlock switched from "brains" to "muscle" in this one.