If during the installation of this game you get an error complaining that it couldn't create a directory in /opt, run the following command:
sudo mkdir -p /opt/revengeofthetitans/full_length_musicThen run the installer again. All this does is create the directory manually, which seems to be all that's needed!
Edit: Looks like the devs are aware of the problem and planning on releasing a fixed installer imminently. A commendably expeditious response!