I'm wondering, what did the Nightmares expansion change? Is it better to do the 1st playthrough without it?

Also, is there a way to turn down keyboard sensitivity?

Play it without first. Nightmares takes place after the events of Blood II. Although it allows you to play the Blood II levels with the other Chosen, it will interfere with the cut-scenes, so things won't make very much sense.

I don't think there is an easy way to turn down the keyboard sensitivity. I may be wrong tho.

Just play it with, it won't affect anything, and you don't have to choose one of the other Chosen.

No idea about keyboard sensitivity, though.

It just seems to be a level pack. I found nightmares to be slightly less stable than vanilla blood 2