See, some enemies won't respond to simple hack-and-slash. Some have shields that need to be shattered with a charged attack, or even with a special gun. Others have weak spots that can only be hit while jumping; in fact, the first boss you'll face can only be hit if you shoot it with a gun that projects laser platforms for you to hop around on. Of course, if all else fails you can pick up debris or other monsters and throw it at them, and that's always cool.
