Yeah that Uplink demo is 100% original level content, even the dialogue. if you've never played it try it as it's a sort of "missing scene" from Half-Life. It's pretty good length for a demo too.
And yeah, this DX leak was *really* impressive. My only complaint is the 3'rd person when climbing ladders and stuff.. but we knew that was coming. In every other way it's full on the spirit of the original game.
Hold off on playing it so you get the best experience when you get the real copy.. just have no doubt you're getting a great game.