I would imagine that a lot of people who use OpenBSD on their laptops/desktops run a lean installation with one of the window managers in base (an ancient fvwm version, cwm which I find very nice and twm).
You can however have a full-fat desktop environment with xfce4 or gnome and applications like libreoffice, gimp, inkscape, audacity and so on if you wish. I've never tried KDE on top of OpenBSD base but I gather packages are in ports.
I think it is fair to say that the amd64 arch has good support. The i386 platform arch is on a 'best effort' basis these days which is understandable. I've never looked at the others.