I want good text rendering and windows and buttons with rounded corners. I want my laptop to work correctly when connecting it to external displays or projectors without a lot of futzing around. I want vsync to work with my monitor out of the box, I want to be able to watch video without tearing, and I want a desktop that has first class support for high-DPI displays. I also want to have some basic integration with the other system features provided by my distro, which increasingly means high-quality integration with NetworkManager and different systemd components. I want to get integrated notifications when a program segfaults on my computer or in case there’s an SELinux AVC denial.

Why not just Fluxbox then?