So what are Cunards Grills all about?

First off, I've never had a chance to stop in one. The closest I've come is walking enviously past the Queens Grill restaurant, craning my neck trying to see how the other half eat.
Secondly, if, like me, you've never had a chance to experience a Grill, (Princess or Queens), don't worry the service in the Britannia restaurant is still some of the best at sea and Cunard are still one of my favourite cruise lines even if I haven't tried a Grill.

Now I know a lot of people get a little offended by the idea of the Grills, thinking it hearkens back to the bad old days of a three tier system, ie first , second and third class. but if you ask Cunard they'll deny this strenuously, stating that their Grills aren't a class system,  you're just paying for extra facilities onboard.
It's all rubbish of course. It is a class system, just based on money rather than birth. But, playing Devils Advocate who can lay hand on heart on say they wouldn't book a Grill if they could afford one?

But what do you get extra with a Grill........?