Genuine question. Why is this game so hyped?

I can totally understand appreciating it if you already own an Xbox, but what I don't get is how people are running out and buying entire Xbones just to play this one game. I mean, for crying out loud, it's just a generic FPS–no different than Half-Life or Call of Duty!

Now there are some deeper titles like Uncharted, Last of Us, Infamous etc. that are built on a more unique premise and that I could understand as system sellers. But what about Halo makes it so different from other FPS's? The story, the gameplay mechanics, what?

I'm pretty ignorant on this topic, as I don't own an Xbox and have only played a couple hours of Halo total. Enlighten me.