https://steamcommunity.com/app/435150/discussions/6/1479857071247883242/
https://www.reddit.com/r/DivinityOriginalSin/comments/74teof/tech_help_cant_rotate_camera_in_the_divinity/
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=633511#Post633511
After the most recent Windows Update, the editor camera is completely broken for some people.
I figured I'd try giving it a shot anyway using the MMB+RMB workaround found in the Reddit and Larian Forums links above. Unfortunately, the bug also kills the user's ability to hold RMB+drag in addition to MMB+drag. This means terrain editing is nigh impossible.
I have tried creating a new project, uninstalling, nothing works. This occurred immediately after reinstalling DE2 after my PC crashed due to a Windows Update messing up.
I'm sort of treating this as a bug report - if there's a better place for me to contact Larian directly (already tried Twitter) let me know.