A new Nintendo hand held means one thing for certain:
A new generation of Pokemon, and this one isn't half bad.
I decided to review this for one reason: I've played Diamond/Pearl a lot. I borrowed a copy from a friend, and I played for about sixty hours, and she got it back, while I had that one, I bought my own copy and again played for sixty hours, and gave it to a friend who really wanted it. This time I'm just going to keep it, because it's a good game, and I don't want to start over again.
The premise is the same as always: Catch some Pokemon and make them battle other Pokemon. Despite popular belief, you can do this in the real world, but in reality this is known as dog fighting, and that is illegal on several levels.
And of course, the story is the same: You are ten years old, you go somewhere and have to pick one of three Pokemon for some reason, and the creepy old guy who owned the Pokemon lets you keep it because it likes you. He then has you collect data of all the Pokemon you can using a magical encyclopedia that fills entries partially when you encounter a Pokemon, and fully when you actually catch it.

The starters are Turtwig, Chimchar and Piplup.
Now that I have introduced the premise and such, let's get to the reviewing part.
A note on the images: you guys are lucky I didn't post any of the anthropomorphic Poke-porn I found searching for these.
Graphics: 5
The graphics contain three basic styles, detailed sprites used mostly for Pokemon. The basic 2d Zelda style used for characters and 3d modes used mostly for buildings. The Pokemon are still cool looking, and even though the new Pokemon from this generation (4) are less memorable than say first (red/blue) or second (gold/silver) generations, they are still worth collecting.

Two of the three graphic styles.

This displays the sprites used in battle.
Sound: 4
The sound effects are still good, the music still conveys the proper atmosphere for a location, and the tune that plays when you heal at a Pokemon Center is still magical. The only issue for sound is the fact that the Pokemon cries still sound like they did in Red, how am I supposed to believe that a living creature sounds like a machine?
[ame=http://www.youtube.com/watch?v=L9X65GoIeQw&feature=related]YouTube - Pokemon Diamond - Pokecenter Secret[/ame]
Replay Value: 5
With 400-some odd Pokemon to collect and train, and the Battle Tower to test your skills at, you can play this game for an unlimited amount of time and still not grow bored of if.
Challenge: 4
It's easy to learn, but the enemies get stronger as you progress. If you play like the developers intended you to (capture Pokemon and level them up evenly, keeping only a few levels ahead of the next gym leader) the game can be challenging, but if you just level up your starter to say: 20 levels ahead of the next gym leader, you can beat the game without even breaking a sweat.
Overall: 5
While this game is nothing groundbreaking, it is still one of the best RPGs you can get on the DS, you just have to get over the feeling of "been there, done that" created by the recycled premise.