One reason people liked the Hulk so much in the Avengers is because the Hulk was actually the bad guy. Now Whedon is obviously a comic book nerd because the 2 villains in Avengers issue 1 was the Hulk who was tricked by Loki into rampaging and a random group of heroes got the call instead of the Fantastic Four.
To make a great Hulk movie Banner needs to be not the hero but the victim and then Hulk is the bad guy, until the very end when he actually defeats some far more dangerous villain.
The first opening sequence of TIH lacked all suspense and conflict because you don't like Blonksy or anyone working for Thunderbolt Ross and you know Banner can't die. This is the big problem. But what you need is to feel for Banner but also not want him around.
If I was writing a new Hulk movie I would cause some reason why Banner can no longer control the Hulk. I would want to tap into Marvel cosmic. Something that can tie us back to GotG. Then I would have Banner when he became himself again send a call for help out to all of his super hero friends something tragic like "Please kill me"
Someone like Hawkeye responds but it could be Scarlet Witch and Quicksilver. They battle the Hulk. Thunderbolt Ross Also gets the call and begins preparations to finally degeat the Hulk. using a great scientist from the comic hopefully Sampson. They use the formula used by Mr. Blue, and using some of Captain America's blood come up with a toxin that they believe will destroy the Hulk once and for all.
Hulk now in a new rampage kills a bunch of children and kills someone that matters to him. At this point a final solution is decided. Hawkeye discovers an encrypted Email to stark from banner explaining that he built a machine that would launch Hulk into space and they just need to trick the hulk into it. With Hulk's lack of intelligence he would never return to earth and the problem with the Hulk would be solved forever.
Hawkeye decides to carry out Banner's wishes.
In the meantime using a helicopter flown only by Thunderbolt Ross, he finds the Hulk while he's destroying a small town. He prepares to fire the missile with the toxin in it but the helicopter is damaged. The helicopter crashes presumably killing Ross. There is a massive fire and a red cloud erupts from the broken missile.
Hawkeye tries one more time to calm the Hulk and this time is successful. Banner returns and apologizes and begs Hawkeye to kill him or use the plan. Launch him into the cosmos. Hawkeye tranquilizes the Banner and brings him to the machine, Straps him down and begins the launch sequence.
In that moment Hawkeye gets a message that something more dangerous and worse than the Hulk is out there. He halts the sequence and runs outside. The Red Hulk is destroying everything, lighting things on Fire with punches, breathing fire and destroying the city that the machine is built in. (Some small midwestern town)
Hawkeye attempts to stop the Red Hulk but is knocked unconcious. Red Hulk destroys the building that the ship is housed in and all that is left is the ship with Banner tied down inside. Red Hulk is about to kill a bus load of children and Banner awakens and realizes only the Hulk can save them He is able to make himself angry enough to become the Hulk. The 2 battle. At the end The Hulk defeats the red hulk but is very hurt and turns into Banner. Banner then beaten and bruised walks into the ship at the end and begins the launch sequence. Hawkeye watches and realizes it's a mistake because the Hulk can do good and defeated the monster known as the Red Hulk but he can't convince Banner the ship takes off the film ends.
Obviously this is just a plot overview and there would need to be a lot more character development. I think introducing the She-Hulk as Banners cousin with no powers, she could be the character that is "killed" and you can do a scene where to save her from her injuries Ross or someone else misguided gives her a blood transfusion of the Hulk's blood making her survive but Green. There should be more opening sequence character development. Have this be a tragedy. Banner never gets to have anything because the Hulk destroyed it. The Hulk needs to be the antagonist and you need to be afraid for everyone else in the universe because only then as an audience is there conflict. Thunderbolt trying to catch bruce, who cares he's the Hulk he'll get out. But the Hulk destroying everything...well there's the problem who can stop the Hulk? No one. So you end up in fear for everyone in the MCU because if they don't stop the Hulk here then it will just get worse and worse.
Though this would preclude the Hulk from being in an Avengers movie it could introduce him to marvel cosmic maybe have him be the enemy in a Nova Movie. Nova Corp vs the world breaker. Obviously this would also destroy the idea of World War Hulk. Unless you can have the Hulk completely take power (possibly Thanos or Loki Magic) and blame the humans for allowing Banner to launch him into space.