Wow, this is pretty cool so far, and a lot of work. I wish you the best of luck with this. I also just realized how old this post is, and hope I'm not jumping in too late.
I would say to keep pushing to exaggerate your character's expressions. It might be worthwhile to do pose studies for emotions and story moments too. With a sort of mainstream animation style like this, I think the emotional and character building scenes would be just as or even more important than your action scenes, and nailing the poses in these would probably be key to telling your story.
Also, don't forget to build up the world around your characters as well. You may have just not gotten to that yet, but it's just as important as the characters. Think of how boring Batman would be, if the story didn't take place in Gotham city.
Hope this helps.