I absolutely love the style of your flat, it's beautiful & cosy, I could spend hours looking at everything there is to see, but you want to sell it so......
I know very little about London and the area you live in, and that being the case I don't know if your home is competitively priced etc, so will just have to go on the basis of the flat itself.
I actually love the contrast of the stark, cold, ugly exterior and the light, airy, stylish interior. That wouldn't put me off at all. It's spacious and very bright. The bedrooms are a good size, as is the lounge. I love the stairs and the layout.
Things that would be a problem for me would be the fact that your lovely stuff could well be covering a multitude of issues, and I wouldn't be able to see it.
The kitchen is a bit pokey for such a spacious flat, and needs work.
So much art/decor on the walls means a million little holes to fill, and as I've spent nearly a day filling little holes in my own walls (with 95% less art!), it would fill me with dread! Plus the plaster might be knackered.
You're on the 5th floor and I have a slight phobia of lifts (although most people wouldn't care).
The door in the kids room. I just don't like doors leading outside from bedrooms.
Everybody has different requirements/dealbreakers though, and apart from my dislike of lifts, everything else could be rectified. It's actually a lovely flat.