It's interesting that the responses you got were all dev related improvements (better line endings, WSL, hyper-v etc.) but I thought I'd try to take a stab at this from a non-power user's perspective:
- Better bluetooth integration (N/A in XP? Unreliable in Win7?)
- Snipping tool (Don't remember if in XP, definitely part of win7)
- Improved automatic driver detection (Drivers were pretty rough in XP, okay in win7 but still needed manufacturer installs for many things)
- Built in camera app? (Voice recorder was always there for audio testing)
- Built in free mail app (outlook always cost money)
- Better out-of-the box browser (windows edge vs. IE)
- Free, good quality firewall (windows defender, came later in Win7 as an update not in XP)
I found it to actually be a difficult exercise which either says something about my memory of the old OS's or it reveals a distinct lack of dramatic changes.