Location, location, location!! What a perfect spot. I visit London regularly and have never stayed anywhere so handy to everything. All shops, transport, restaurants, etc. were literally on your doorstep.
The flat itself is a very generous size (esp for London) - the lounge and dining area super comfy and relaxing with beautiful windows overlooking the street below. Despite being in a bustling area, the noise was never intrusive as the bedrooms are in the back overlooking a little-used courtyard.
The flat had everything we needed for our stay and very comfortable to stay in.
Best was the easy communications with Guy who readily answered any query we had and also kept us well-informed leading up to our stay. I would highly recommend (especially if you're doing the theatres/Covent Garden/shopping.)