...So I beat the final boss and it just cuts to an animation of him exploding while my character makes pain sounds in the background. At this point there is no way to continue / exit without bringing up task manager. I was hoping for a new game + or something, or at least be sent back to the workshop... am I missing something?

It's a bug, I had it as well on my first run. You can replay the final level via main menu to try to get the ending sequence.

Nah, played on the initial one when it happened to me.