I liked the planet Hulk comic and movie just as much as anyone else. I also liked the World War Hulk, however that is a horrible way to go with the live action movie universe right now. Still there would be an easy way for them to do it.
One simple but important word. Ultron. The Avengers: Age Of Ultron is coming, that we already know. Ultron is smart, and a has the ability to control and make technology, for instance Vision. He could easily decide that Hulk is his biggest threat make a space ship shoot him off into outer space, but that leaves the other Avengers enough time to beat Ultron while he is distracted with dealing with the Hulk. Ultron is beat and can't control the ship which causes it to go off course and land on Sakaar. World War Hulk? Easy, Iron Man is trying to get rid of all traces of the Ultron program and accidentally causes the ship to explode. Now Hulk is mad because they didn't try to help him despite him being a hero, and they killed his family. Fairly simple, but the problem is, Planet Hulk is all Hulk all the time. Mark Ruffalo is a fantastic actor who plays a good subdued Bruce Banner while still being extremely expressive and tortured. His gorilla-like Hulk was awesome and the one time he did talk was one of the highest points of the movie. He was a good guy in the end and after he wasn't needed he went away. No one would currently benefit from him going to space.
What they're doing wrong with the Hulk is that every movie he has some weird convoluted plot. The Incredible Hulk went in the right direction with making a lot of action, the Hulk movie went in the right direction in exploring the dynamic of Bruce Banner and the Hulk. What needs to be done now is a lot of action in between exploring the relationship of Bruce Banner with the Hulk. The Avengers tv show did something interesting that the first Hulk movie attempted to approach. Bruce Banner able to talk to the Hulk by looking in mirrors and reflective surfaces. It makes sense because he is a mirror of his inner demons a.k.a. his anger problems. He is a version of him without inhibitions, he is purely instincts, full ID just pure anger and sex (proved by the attempted sexual contact with Betty in Incredible Hulk and his harem in the Ultimate Comics). Bruce Banner and Hulk need to come to a place where they attempt to understand each other. The Hulk coming out for the safety of Bruce because he cares rather than self interest. When they come to a place where they recognize that they are both separate entities and completely different personalities they can reach an understanding with each other to where Banner can trust the Hulk enough to turn into him because he wants to. Take a break from having him running away from the government and show him in a crazy situation that isn't even really centered around him necessarily and how he and the Hulk have to deal with it. Maybe have him having to take care of a child who is being sacrificed or something. Show some new people.
Hulk and Hawkeye
Captain America 2 gave us a rare sighting. We got to really get a more in depth look at a secondary protagonist in Black Widow. You really learned a lot more about her and began to enjoy her more as a character. She wasn't just an ass kicker she was an interesting person underneath. The Hulk needs another movie and I personally don't believe the current state of Hawkeye gives him enough character depth to actually get a standalone film. Sure a lot of people probably want to see it but what do we really know about him cinematically that would be of interest. The big 3 (Iron Man, Captain America, and Thor) came out in their own movies to start then showed up in minor spots. Hawkeye and Black Widow didn't. Hawkeye and Hulk had an interesting relationship in the Avengers cartoon, first they were enemies then they were reluctant allies and then they were friends. You have a lot of Hulk villains or villains in general who haven't been used. What I imagine is having a gamma world movie. A bunch of innocent people are turned into gamma monsters by the leader. Hawkeye has Bruce make him gamma dampening arrows while Hulk takes care of the big guys, The Wrecking Crew or Abomination or Absorbing Man. Show them dealing with their relationship Bruce viewing Clint as a lapdog for S.H.I.E.L.D. and Clint viewing him as a monster in sheep's clothing. They grow to understand and respect each other. Use this time to introduce other characters like Rick Jones, use gamma world to bring in Doc Samson, much like Cap 2 bring in Falcon. Give the Hulk movies a little love and the right cast and directors and he could be a perfect part of the marvel franchise.
They've already done a good job with Hulk and the agents of S.M.A.S.H. showcasing new characters. With the success of Guardians of the Galaxy, they've proven they can make an interesting story with characters nobody would expect. Do it with Bruce Banner. Then once they show more personality to Hawkeye then give him his own movie and make it great.