An excellent experience. Went for my 52nd birthday, with grown up kids (who have all watched the TV series) and a visitor from abroad who had never seen the show (but we did give her a quick explanation, and she thoroughly enjoyed it!)
The actors are excellent, really getting into the role. Sybil's laugh, Basil is grumpy with the diners, and Manuel doesn't understand anything. You can see the jokes coming, especially with the slapstick, but everyone laughed all the way through the lunch.
The food was quite acceptable (nothing special, but no issues) including the vegetarian option. Drink costs quite acceptable, bearing in mind it's a London hotel!
Overall a very enjoyable experience, highly recommended!