I really like Wagamama as a chain, but Wagamama Knightsbridge is horrible. It's full of annoying shoppers and there's just no atmosphere to the place at all.
Avoid it - it'll put you off Wagamama for life.

We stumbled upon Wagamama on a rainy Saturday afternoon while sheltering in Harvey Nicks. It was 2pm and the queue was all the way from the restaurant to the street but we decided to wait and were seated within 5 minutes. The staff were busy but great and the trip was made worth it in the first few minutes after receiving two ice cold Asahi beers - just what was needed.

We ordered Cha han, Yaki Soba and Duck Gyoza - all absolutely delicious, especially the Cha Han. On the downside - my partners meal arrived quite a long time after mine and we had to remind them about it. Also the ladies toilets didn't flush and obviously hadn't for quite a while....
We did thoroughly enjoy our visit and would definitely go again. Cheap, delicious and fast! Loved it!