FullMetalOtaku
Regarding your point about "opening your novel with an action scene because no one cares about the world or character," I've got another point to add.
I did the exact same thing with my novel (not the vampire one, but this one - shameless plug, haha)
I first jumped straight to the action scene. But then I realized if readers don't know who these idiots are, why would they care?
Then I went back and write 4 chapters to introduce each of them as proper human beings. At that point I feel that readers will be more interested in seeing them succeed.
That said, you might be able to hook readers in with an ultra awesome fight scene. But if you are not sure you can pull it off, then introduce your mc first.