OK, I'm laughing at the commonsense review that says it's somewhat educational because your kid will learn about Vikings. I'm pretty sure that real Vikings don't have much in common with the characters of this movie, but maybe I'm mistaken. Did real Vikings spend a lot of time fighting dragons?
I went to see it with my 11 year old and his friend. We thought it was great. I think it would have been to much for my particular 4 year old, who often found movies on the big screen overwhelming. It's very fast paced and visually stimulating, and involves a lot of scenes where children are in mortal peril from dragons. On the other hand, if you have a kid who has enjoyed other fast paced action movies on the big screen I'd say go ahead and try it out. There's nothing really innappropriate, just a little intense.
The other thing we thought was weird was that other than the names of a few characters this movie had almost nothing in common with the book. We loved the books so that was a little weird, but once we decided to overlook that we loved the movie too.
And of course, they'll learn all about Vikings!