boot>
What am I supposed to do here? Does it require some weird incantation in order to load the kernel? It turns out you just have to hit enter.The OpenBSD install script really is quite simple. I'm not sure I would call it easy (simple ain't easy), but it's certainly straightforward and setup is usually just hitting enter a bunch of times. You only encountered trouble because you tried to fiddle with it and got frustrated.
Another huge benefit of OpenBSD compared to Linux is the incredible quality of documentation. Missing or outdated docs are considered a serious bug. To address your issue, let's look at the docs: https://man.openbsd.org/disklabel#AUTOMATIC_DISK_ALLOCATION
It looks as though if the installation target is smaller than 8GB, it won't create a separate partition for X11. That's useful to know. Additionally, you can specify your own partition template using the -T option.
It might be cool to see a graphical project like GhostBSD built on top of OpenBSD, but I have to agree with the curmudgeons that the text-based installer is pretty fantastic as-is.