UI is garbage, from right click to the taskbar, its a alpha release being sold to as complete product.
settings missing alot of control panel items and you cant go back in some cases for even simple things like sound device management, network management, all settings are far far from parity.
Poor hardware compatibility, bsod on same hardware is common occurance.
Privacy invasive spyware. From the search service to the telemetry. Its a data mining platform
Security is terrible. Internet connected Services are on by default that shouldnt be like search and telemetry. Any on by default service, like telemetry can and are abused with zero days. Mandated cloud services as a bandaid to poor local account security. Security is a bandaid full stop, from the kernel to cloud services its not secure by design.