That's probably for the best. There's only so much you can do with the Hulk on his own in a cinematic format -- he works best in a supporting / occasionally antagonistic role.
Yeah, unfortunately I think the two movies proved that Banner just isn't really interesting enough for his own movie. You either have way too much tiresome angst as he searches for a cure and pines after Betty, or you're watching a green monster growl a lot while destroying stuff.
There's just not a whole lot to work with.