As stated in other reviews, men require a dinner jacket. My wife and I decided to try this restaurant based on a TimeOut review. It didn't mention the formal clothing requirements so I was just wearing a patterned shirt and smart trousers, but I was provided with a jacket on the door and we weren't made to feel out of place at all. I just wish I'd chosen a shirt that looked better with a jacket!!
Once we were seated, we were presented with a fixed price menu and we made our choices. The food was excellent, as was the service. I had lobster ravioli, followed by duck then the souffle. Echoing other reviewers, the duck was exceptional and the highlight of the meal for me.
I'd highly recommend Le Grenouille. Just make sure you wear a shirt that looks good with a jacket, or be prepared and bring your own.