So it turns out that OpenBSD 7.4, specifically the amd64 version but possibly others as well, really doesn't like it when i set the root password to:
qU+wFoM"%=J@s4j" When i do so, it doesn't let me log in as root -- but when i use `su`, i'm able to become root and change it to a password that does work. This is all on a fresh install, setting this password in the initial setup wizard. Maybe one of the special characters is breaking it?