Serebii.net is probably one of the better sites to get more information including screen shots:
http://www.serebii.net/diamondpearl/
The graphics have been enhance, but nothing ground breaking, real time clock is back run off of the DS clock. I haven't tried the stylus controls so I'm not sure if they add anything. The mechanics of the story mode so far hasn't strayed very far from what has been in past games which is a good thing if you are looking for more of the same, a bad thing if you were expecting something revolutionary.
To me and to a lot of others the big deal about a new generation of pokemon games are the new pokemon/type combinations/moves/mechanics/etc that it brings and the strategic depth that adds to the already very complex battling system. I will be buying copies of the English version as soon as it hits the shelves.