Well, I'd have to agree it's pretty unsuitable. Blood and guts everywhere, and some fairly heavy innuendo (though no full-blown CGI sex, not quite...). It's more the sort of film you'd take your teenage son to, and you could both enjoy for different reasons (though those wretched helmets do obstruct the view). It takes a few liberties with the plot as well, so probably not an ideal introduction to a great classic of Eng. Lit.
Having said all that, I took my 8 year old and he enjoyed it.