I'm not really a tv person anymore - Too much drivel.
But a good movie I can really absorb. The depth of the spoiling matters a lot. If you know they all die or the hero is the villain, then it can be a bit pointless - It's just for the aesthetic pleasure then, which would bore me to tears.
But having a brief insight into the workings isn't such a bad thing - It can get you interested. A good trailer can often mislead too.
I watched 'Amistad' recently, and '2012'. The former was outstanding, the latter was crap.