You may not have noticed, but there are two new names for the two main legendaries in the Shinou Region. these are the ones on the covers.
Dialga- Dialga has the power over time using the diamond shaped symbol on his chest.
Palkia-Palkia has the ability to warp space with the pearls on his shoulder.
Other new gadgets and what-not:
The Poketech- The Poketech is kind of like a wristband. As its name implies, it is a technological device used by trainers. It allows you to interact with certain gadgets and settings via the touch screen. Its functions aren't as good at first, but you can earn more by continuing on your adventure.
Your Rival- Instead of just battling you in parts of the storyline, your rival, this time, will usually help you. In fact, sometimes you'll have to work with him to complete certain tasks. He will sometimes battle you though.
Manaphy- The first time you can gain a new pokemon by playing a non-rpg version, Manapy can be caught in Pokemon Ranger, then transfered to Pokemon Diamond/Pearl. A special move used only by Manaphy, Heartswap, can switch healing moves.
That's all I'll reveal today. I'll give you more info as I get it.