It has baffled me that Marvel thinks Hulk is so unadaptable to screen. I think he´s such a great character and so rich in terms of what you can do with him. However it is true that he does lack a seriously challenging villain. However, I think the best way to go with a Hulk movie is have him face Sentry. Why?
I think he´s the greatest foil to Hulk, a superpowered schizophrenic superhero so corrupted by his own immense power that he begins to see humanity as mere ants and himself a god. At first Shield want to use him, Banner and him can even work together, but slowly he begins going mad and Banner sees this warning Shield. They don´t listen and Sentry goes on a rampage, only one being on the planet even has the remote chance of stopping him, Banner must embrace his inner beast.
Tell me that isn´t a synopsis and a half for a Hulk film. Plus it will give comic fans the closest they´ll ever see of the battle of all battles, Hulk Vs Superman. Everyone and there mother will have to watch it. What do you think.