Playing the demo right now. So far the interface and controls are smooth and elegant, a bit different from the previous titles (though each one has always been different from the other) but the fluidity is essentially intact.
The "mark and execute" feature is so badass to watch. You earn targets for it through hand-to-hand stealth kills, which are varied in animations. This iteration of the Splinter Cell game deviates from the others in that killing targets is not penalized in anyway (basing it on the demo) and it's natural in the story this time around (rogue, vengeful Sam).
The graphics are superb as always, and on a larger HDTV screen (I played the first SC on PC, subsequent ones on analog TV) it lends a cinematic edge. The in-game environmentally presented directives are kinda cool but they're a bit too pronounced; I'd turn down the distracting whiteness of the text if I could.
The demo doesn't really spoil anything much. The emphasis is on the gameplay, so it won't hurt to play it.
Overall it just feels very modern and sleek.........and yes, sexy. But then I have a very personal vested interest in Sam Fisher.