I liked the film first off. How you used the comic book idea of knowing what the character is thinking is great! We don't see that in many other films, but that was done very well. It brings you more into the story.
A few things you could've worked on...blocking is one of them. Sometimes it looked as though the actors didn't know what to do once they reached their mark.
The script seemed strong. I'm not sure where you are going with it, but it seems like a good intro to your world of Batman.
I'm not sure if the Joker would kill Batman. After seeing "The Dark Knight" (which it seems that this is inspired by) the Joker wouldn't kill him. Like he said, "You're just too much fun!"
The hostage wouldn't be in the same room as the Joker. He would only take a hostage if the Batman crashed his plans and he would use the hostage to get away. Not to set Batman up in a trap. He would use it as a diversion, but not a trap.
I wasn't into using both themes for Batman. It almost seemed the character had two cues. One being Zimmerman and Elfman. One or the other. It didn't work very well. Or just don't use a theme at all. Silence can be just as effective.
Other then that...good job and good luck.