For me, how they handle the story is often more interesting than the story itself. Reading a script isn't the same as seeing it played out on screen, and that's where a big part of my enjoyment comes in. It's not a totally new concept, either.You don't want any surprises? I'm crazy tempted to know everything, but it would ruin the campaign, for me at least.
Although hasn't the majority of the plot been accidentally shown?
I don't actively seek it out, but if I read something, it's not the end of the world. I knew about the Arbiter going into Halo 2, and I was excited to see how they made that jump.