We recently got our windows replaced in the house.
In terms of design we literally replaced like with like i.e. brown windows with leading squares.
But in terms of efficiency we replaced with much better. We had got wooden, single glazing windows, these new ones are now pvc and double glazed. The difference they make to the preservation of heat in the house is palpable. So I am confident that we will see the difference in our utility bills this Winter.
Also, what is great is that they will not need any maintenance. The wooden onces needed repainting every couple of years or so.
I am very happy with them! We also got the exterior of the house painted at the same time. So all in all the house looks reasonably smart in my opinion.