This was definitely the right way to go with the story and end the series. However, I'd have liked to see more action for the climax. Especially with the Guy riding Mancubus, both with guns ablazing, as that was awesome and kind of adorable. Even if it was just the black and white style of the credits, I'd have enjoyed seeing the DoomGuyMancubus combo wreaking havoc.
It just felt kinda short for an ending. It was good though!