This movie has less depth than Paris Hilton. It's basically a very old John Wayne going to Britain and kicking butt just the same way he's done it in dozens of previous films. BUT, on that level, it is a very good and enjoyable film. In particular, the film had wonderful "Dirty Harry-like" lines and a dark sense of humor. In fact, I half expected him to say "make my day"--it was so much like an Eastwood film. And, the film was much better than Wayne's previous attempt to knock off Dirty Harry in MCQ. So, provided you can also turn off all sense of disbelief (after all, Wayne was WAY TOO OLD FOR THE PART), you can enjoy it much the same way you'd enjoy one of his older flicks such as THE FLYING TIGERS or THE FIGHTING SEA BEES. In other words, this is a 70s version of an old Republic Pictures action film--with a few updates to reflect the times (such as Wayne being saddled with a "dame" for a partner). Overall, if you hate John Wayne films then I'm sure you'll hate this one and if you like him, this film won't disappoint. It's just good old-fashioned fun!
By the way, according to Robert Osborne on Turner Classic Movies, John Wayne was offered the role of Dirty Harry BEFORE it was given to Eastwood! You could tell Wayne wished he had taken the part since he soon went on to make his own variations on the genre.