It took me forever, literally, to get to the entrance killing everyone without causing an alert or let someone find a body. Some of those patrol routes are devious...
But with the Strong Draw Weight on the Bow, you can actually shoot bodies into hiding spots. First time I shot someone with the SDW and he flew then slid about 15 yards into a dark corner, I just had to smile.
I also like the 3D. I wasn't so fond of the level design early on, a lot of those ledges you'd think you could scale you actually can't, but the sneaky stuff was nice - and above all, consistent. I knew when I made a mistake, knew where how and the AI would react. Very nice.
And this just goes to show that the campaign can indeed get pretty long...