I too want to see Dr. Doom done right.
I think an Iron Man movie would supply a better origin for his character (independent of the Fantastic Four). Imagine if Rourke had played Victor Doom in Iron Man 2 instead of Whiplash.
Doom could have lead right into the central villain in The Avengers, whether Kang or Thanos.
I voted for Kang. I'm sure that Banner will be what the Avengers are brought together to capture at first, but a greater villain will emerge.
Kang is powerful enough to fight all of the Avengers: Captain America, Iron Man, Thor, and The Hulk; and Kang doesn't require the audience to accept a space alien into the plot as with Thanos.