Pearl and Diamond are the next Pokemon games and like ruby and sapphire, are too similar to the previous installments
There isn't much new stuff here, which is the biggest problem. The touch screen is used in battle and feels better, but doesn't really change much. The clock from gold and silver has returned as have the day and night affects, which is great news. The bottom screen when you aren't battling is useful, you can use if for the clock, checking stats, or playing fun little mini games even. It isn't much, but is a nice touch.
Diamond and Pearl also have a very cool underground part, where you can connect and play multiplayer. You compete to dig for treausre and can actually dig in the same place at the same time. You can also set traps and steal someone's findings so it is a fun new mode, my favorite part of the game.
Online was also added in this installment, but it doesn't really add much. You can auction your Pokemon and bid for Pokemon online which is pretty cool, but you'll rarely find a good auction for you as most of them are just bad trades. Battling online isn't really fun either, because there are so many different people that you typically won't find someone that will give you a good fight. So, overall, I felt that online was not meant for Pokemon.
That's really all when it comes to new features, you're still collecting 8 badges, still stopping some evil organization, still battling the same way.
I would also like to say that Pearl and Diamond have more replay value than any other Pokemon game. There are tons of legendary Pokemon and new ares to go to after you beat the game, which is a big plus.
The sound is pretty good, the graphics are a downfall though. It's still plain 2D despite the 3D graphics at some parts and the animation could be better, just feel a letdown in the graphics department.
So to sum things up, Pearl and Diamond keep the Pokemon formula the same (sadly) but add some neat little tidbits that make the game just a bit better then the average Pokemon games, if you're a fan of Pokemon, you'll want to pick this up.
Final Score: 8.25 + cave & replay value (0.25) - graphics (0.50) = 8.00