More games ran on it (mostly thanks to higher DirectX version).
From developer perspective, XP was the first version of Windows with registration-free COM and side-by-side assemblies, which (if used properly by app devs) fully solved the "DLL hell" problem.
IIRC it was almost always the video card driver; I ran W2K for quite a few years into the XP era before moving to XP with 2K theme. Everything was happy except the video card drivers, which were often "XP-only" but actually worked fine with 2k.
Taskbar grouping.
ClearType.
Remote Desktop.
More games ran on it (mostly thanks to higher DirectX version).
From developer perspective, XP was the first version of Windows with registration-free COM and side-by-side assemblies, which (if used properly by app devs) fully solved the "DLL hell" problem.