If you have any skills in FPSs you should play on at least the Advanced difficulty. I have played a few run throughs and each time had an "Oh shit!" moment. I haven't been able to predict what the Director is going to do yet.
Beta or demo? I heard the reason you can pre-load this now was there was an exploit on the Gamestop site where you could trick it to give you a beta key. Valve noticed the rate at which people were getting in and stopped all downloads for it.
I know about the demo and am playing it. I just heard in other places that there was a beta and I haven't bothered to find out myself.
I am legend vamps are super super fast, 28 days later they just run all the time. and I am legend they notice light in dark rooms.
That is if my computer can actually run it, even though it is installing right now. Supose i'll let you know how my measly 2.8ghz comp stood up.