Although not a long jump from the rest of series, Diamond offers a solid experience and some very addictive game play.
With that out of the way, I can continue on to the real "meat" of the review.
Pokemon Diamond does little to advance the series in the way of graphics and game play. The system remains the tried and true battles of old, and the graphics, although slightly improved, are still akin to Emerald version. The story starts with our hero helping the Pokemon professor out of a tight spot, and as a reward, receives a pokemon for his efforts. After you pick one of the three possible Pokemon to start with, you are off on an adventure to become the best trainer in the land. Many familiar Pokemon make appearances throughout, but there are a plethora of new species as well. To top it all off, many new evolutions have been added for older pokemon, such as Porygon Z. One particularly nice feature about Diamond & Pearl is the fact that you can port over Pokemon from any of the GBA versions. Simply by inserting a GBA game cartridge into the appropriate slot you may carry over six Pokemon a day via the Pal Park. In my case, this became a motivator to go back and play the GBA versions so I could increase my Pokedex. Add to this the recent release of "Battle Revolution" for the Wii, and you have quite a large universe in which to feed your Pokemon addiction. In conclusion, Poke-addicts and newcomers to the series alike should find plenty to keep them occupied in Pokemon Diamond.