My biggest issue that would stop me from returning was the cheap mattress on the bed. It was really awful, you could feel the coil springs as you turned over so neither of us slept well at all. To me, this is key in a great apartment, if the mattresses are an afterthought and you end up not sleeping well it ruins the entire stay so they definitely need to be replaced. (and as mentioned, it's an approx 54 inch wide bed, which is a UK double size, not a UK King as described in the listing)
This was an ok apartment and it was clean and tidy with modern furniture. It is small (but it's London, so I get that's why) and there is no space in the master bedroom to store suitcases or bags, or clothes, so pretty much everything was in the living room.
A minor issue was in the living room, there were four of us but the only place to sit (unless you include dining chairs) was on the sofa which really only sits three people comfortably. Might be nice to get a smaller circular dining table and add an armchair. Also, a net curtain or a different sort of window covering would be good, we basically sat with the blinds down the entire time as we are at street level and everyone passing could see in the house.