Excellent, loved it but needed to watch it at least twice to comprehend the backstory. However, on each occasion, I became more impressed by the stylistic period flourishes which even extended to the tractors residing at Picton's Intelligence Base, the art, furnishings, clothing, music, etc. Yes, I admit to some nostalgia.
Ended up reading the book which is even more complex & detailed & am a definite fan of Le Carre now!
But why did they change the ending somewhat? Charlie ended up with significant post-traumatic stress symptoms & was considerably emotionally disturbed by her experiences, IMO.