Georgian proportion is the reason these rooms still work. Everything else, the colours, the furniture, the fashion for stripping things back, has changed several times over, and the rooms keep absorbing it.
The proportions are the design
Ceiling heights, window placement and the relationship between the two follow ratios that were applied consistently. Windows diminish in height on each ascending floor. The principal rooms are on the first floor, where the ceilings are tallest.
A room built to these proportions is difficult to furnish badly, which is the practical reason Georgian houses are so persistently desirable.
Shutters, not curtains
Original panelled shutters fold into the window reveal and were the primary means of controlling light and heat. Where they survive, they are worth repairing rather than covering.
They also change the room twice a day in a way that fixed curtains do not, and they keep the architecture visible.
Colour on the walls, restraint elsewhere
The drawing room here is a pale grey-green, which reads as almost neutral in daylight and goes considerably warmer under lamps in the evening. Broken, slightly chalky colours behave this way. Flat modern emulsion mostly does not.
Against that, the furniture is sparse. Georgian rooms were not crowded, and filling one to Victorian density immediately reads as a mistake.
What a restoration should leave alone
Uneven floorboards, slightly wavy glass, plaster that is not perfectly flat, and paint that has built up in the mouldings over two centuries. All of these are routinely corrected, and correcting them removes the reason the room is worth having.
The best restorations here are the ones where it is hard to say what has been done.