I feel like the window manager is important, but for newbies I also consider the package manager and overall installation process to be very important.
I’ve had pretty distros that are basically busted after a package fails to install or video drivers are mucked with. An advanced user could fix most of these issues, but this is usually where a new user may go running back to their previous OS.
A good computing experience for me is all my hardware working with minimal fuss and all the software I expect to be available being a few terminal commands away (e.g. steam, developer tools, etc.)