in 5 minutes the following comes to mind: performance, efficient usage of system resources, stability, file system, decouple GUI from core, decouple apps from core, simple remote access, get rid of the sick registry, customization, documentation, adhere to common open standards, lower hardware requirements, better modularization, remove unneeded services/bloatware, provide a powerful shell, enhance security/permission features, ...
I'm sure I can find a lot of other stuff that's wrong with windows when thinking about it...