downloaded the demo this morning and i love it!
it was indeed short, but of course, it's a demo so i didn't expect much... what i was surprised about was that they did not include a demo of the Denied Ops co-op mode, i was pretty excited to try that out with a friend.
what i don't like so far are the controls, a little awkward and different for Splinter Cell. also, another thing that bothered me was the delay from when you stealth kill a person to when you get your marks available... i was in the sewer portion right after i watched the scene and i took the path through the mini tunnel to stealth kill the guy there (after he finishes talking), my mark meter didn't appear as fast as i'd want it to, which caused the other two gaurds across the room to notice me, fire a shot, and thus alerting the guards even further down the tunnel. it just isn't as fluid as i thought, hopefully this will be fixed in the final product.
next point, i was skeptical when i heard that you don't rely on sneaking in the shadows that much anymore since Sam is rogue now, but nonetheless, they pulled off the new sneaking system pretty well with the screen turning black & white when you're invisible.
overall, i think it's a pretty solid demo and things are looking good for the game. i'm even more hyped up for the release now, already have my Collector's Edition pre-ordered