First off, I'm not a huge children's movie fan, but this one was just so charming and cute I couldn't help but like it. The real star is the BFG. The funny way he talks and the emotions on his face really made the movie for me. The little girl does a pretty good job as well.
This isn't the kind of movie you watch for the story. It's simple enough, but does the job. It's more for the interaction between the girl and the giant, and in that department the movie delivers. Sure there were some childish jokes, but there were plenty of other moments that made me laugh out loud without involving body functions.
I don't get why so many people hated on this movie. Where they expecting Schindler's List? This wasn't that kind of Spielberg Movie. It was more about the interaction of a child and magical friend, akin to ET - and while it may not be quite as good, I still got a lot of enjoyment out of it. If you don't think you're going to be a stick in the mud about it, go ahead and give it a watch. You might end up being surprised at how much you like it, just like I was.