That last one looks a bit urban, so I would keep up the work on that.
Maybe break that semi blue back 'wall' apart, and create some type of building shape. Actually, heres a suggestion (an idea, if you will) - make a 'wiggly' building to match the style of these backgrounds that basically nothing is straight.
Idea 2 - make some type of person shape, and totally 'wiggly' it out. Innocent bystanders watchin' the fight? That'd be cool.
Other then that (idea 2 is kinda stupid, but it'd be cool) I love this one.