I agree; the original seats in the Mk4 were rather more comfortable than the current seats; the only thing wrong with the original interior was the silly glass partitions.
Thank god, I'm not not alone after all. The Chapman seats used for the Mallard rebuilds are shockingly uncomfortable. Yeah, they look good but they are too low slung and too shallow for comfort. They are top of their class for 'numb bums' due to the curvature between base and back and the plastics seem to be wearing very badly. I've never tried the Chapman First Class seats but they appear to be almost identical in design but for being wider and having the recline option.
The original IC225 seats were well raked, well positioned and their lower back height allowed a view around the carriage and out the windows. I'm pretty sure the airline tables were larger than the Chapmans too. The full size tables were certainly wider. The spacing of the luggage racks originally was far superior also with mid coach storage.
I know they weren't popular but I also liked the smoked glass partitions. They improved the ambience and helped to zone the carriage and 'localise' noiser groups or families.
The GNER refurbishment would have looked great and been comfortable if they had kept the original layout (whilst allowing for DDA improvements) but just refoamed, retrimmed and powder coated the original seats in the colour scheme chosen for Mallard and replaced the carpets, lighting and luggage racks etc.