I keep coming across really good eating places which don't really fit into the "restaurant" category and yet are little gems. These are rarely listed on Tripadvisor and some contributors are probably put off by not finding a suitable category to place these in.
So how about broadening out "Restaurant" to Eating places and a special category for "street food". There is a growing trend for quality street food in London and the concept is already well established elsewhere around the world.
One such hidden gem is situated next to Trocadero. Easily missed, but it serves authentic Indian street food as ridiculously low prices. I can list many others. None are on Tripadvisor.