Rating for the Food Hall alone, which has a genuin...

Rating for the Food Hall alone, which has a genuinely amazing selection of <intake of breath>

Gluten-Free food from the Beyond Bread 100% GF stand concession
Gluten-Free cakes in the Selfridges fresh bakery counter
Gluten-Free meals & treats in the chilled section
Cheeses (from the renowned Mons cheesemongers)
Fruits (they routinely have kumquats!)
Packaged teas, from the likes of Teapigs
Expat foods from Australia and US in particular, Tim Tams!
*Fine* chocolate in the Chocolate 'Basement' downstairs from the Food Hall

Visiting roughly once every two months, there are almost always new things to see and try, and often stalls offering samples too. Almost always worth visiting :-)