I have been shopping at Topshop for a number of years and have had mixed experiences.
Shopping instore I have always felt a bit judged by the staff, I am a size 14, and feel out of place shopping in store, and therefore prefer to shop online.
I used to love their Joni jeans and found them to be good quality. However, recently the fabric changed and the quality was terrible. After a couple of washes they stretched and fell apart. I took the jeans to my local store and managed to get a full refund.
My experience with the online team has bend very mixed. I once made a complaint after my local store lost my order. After 8 phone calls and a month of chasing, no one ever phoned me as promised. Very disappointed.
On the whole I think topshop has high prices and medium quality. I have moved away from this brand in the last year and have found better quality for the price elsewhere.