a criminal virus there is no other way to describe it.
Bloated, unintuitive, cumbersome, weighed down by backwards compatibility with older hardware.
Its also badly designed
Malware is too easy to install; system is easily corrupted; the registry is a nightmare; uninstalling apps leaves debris all over the place; inability to fully manage disks (partitions, formatting) from within the Management console - you need to resort to the command prompt and use DISKPART.
Viruses abound. Malware left, right, and centre. Passwords are easy to extract form the system (presumably the registry.)
and unbelievably ugly in design.
Inconsistent icons; inconsistent program layout; For window 8.x, having a touch interface on non-touch devices is burdensome;
The whole reason people use it goes completely over my head.
See previous points.
Windows Phone is completely different, though.