[cosmic_cheese]

I really liked XP (and 7) because for me, having a capable theming engine built in that didn't take a ton of extra resources or cause instability (unlike Stardock's WindowBlinds) was a real value add. There were some absolutely gorgeous third party XP/Vista/7 themes on sites like DeviantArt that worked extremely well within the limits of the engine, had a unique look and feel, and were just as usable as the "classic" theme.

When MS gutted the theming engine with the release of Windows 8 (flat rectangles only) I was devastated.

[DaiPlusPlus]

The engine itself isn’t gutted - it’s full of functionality that was never lost. MS just (correctly) reasoned that transparency effects in the UI - introduced in Vista simply to show-off the capabilities of the DWM compositor - ultimately detract from a good UI.

[cosmic_cheese]

From what I remember it lost the ability to render rounded window corners, because while Windows 8 msstyle themes existed they all had the hideous boxed corners that clashed hard with many looks.

I don’t agree that transparency is always a detractor. Judicious use can be a net positive, but it doesn’t work for all themes and there should be an option to turn it off. Personally I didn’t find the W7 variation of Aero to be bad at all.