I saw an interview recently where even Stan Lee said he was disappointed in the way Doom was handled in the movies. He ought to come back and come back in a BIG way. I don't care who he goes up against, whether it be the Avengers, solo or team, F4, Spidey, or X-Men. Just do it right.
BTW, Loki put on a really respectable villainous turn in the latest Avengers movie, full of nuance and venom. And the next villain is ... (not Doom) :(