The first WSL was a Linux system call emulator using Windows NT kernel's multi identity features. While it is an impressive feat of engineering showing off NT's strengths, many of the syscalls were missing. The programs had to operate on Windows file system which likes bulk operations and try and fail kind of a pattern. So it was slow.

WSL2 is fantastic. It is a lightweight Hyper V VM so programs run at native speed. You can do nested virtualization with W11. The file system is ext4 on a virtual HD file so, progams optimised for Linux don't suffer. It even comes with its own Wayland compositor running on top of a high performance GL <-> DX translation layer. It comes with systemd support so one can run regular systemd services like nix daemon.