This is the best game ever!!!
The games contains 107 new Pokémon and chronicles the adventures of a new Pokémon trainer who vies to become the Pokémon League Champion, collecting and training various species of Pokémon along the way. As in most games in the series, Diamond and Pearl feature eight Pokémon gyms led by Gym Leaders, professional trainers whose expertise lies in a particular Pokémon type. Gym Leaders serve as bosses and reward skilled trainers with badges of merit, key to the advancement of the plot. The protagonist must simultaneously thwart the agenda of the criminal organization Team Galaxy.
Diamond and Pearl begin in Futaba Town. After viewing a television report about disturbances at a distant lake by a red Gyarados, which could very well be the same Gyarados that appeared in Pokémon Gold and Silver at the Lake of Rage, the protagonist and his/her rival travel together to investigate the local lake. They spot Professor Nanakamodo, an expert in Pokémon evolution, and the protagonist's second rival, who is the opposite gender of that selected. After a short discussion the pair exits from the lake, leaving a briefcase behind. The protagonist and his or her rival examines the case when they are attacked by Mukkuru. The player is then given a choice between three Pokémon found in the briefcase, Naetle, Hikozaru or Pochama. After defeating the Mukkuru, they return the briefcase to Nanakamodo. Noticing that a bond has been forged between the young protagonist and his/her chosen Pokémon, Nanakamodo offers it to him/her, asking that he embark on a journey and fill his/her Pokédex.
As the plot continues, Team Galaxy's motives are made clear. Executives of the organization are named after planets in our solar system, such as Mars and Saturn. Team Galaxy captures Yuxie, Agnom and Emurit, of Shin'ou's three lakes, and imprisons them, making it the player's responsibility to free them. Upon releasing the trio, one is able to travel to the sacred shrine atop Tengan Mountain and enter the cave, where the leader of Team Galaxy awakens either Dialga, in Diamond, or Palkia, in Pearl. Dialga and Palkia's powers begin to "overwhelm" Shin'ou, causing the newly free Yuxie, Agnom and Emurit to attempt to stop them. It is then that the player is able to engage in a battle with either of the legendary Pokémon
Within a species, Pokémon feature slight aesthetic differences depending on gender, including aspects such as differently sized or absent distinctive physical features. For example, a female Wooper has smaller antennae than its male counterpart and a male Scizor a smaller torso than a female. New abilities, such as "Belligerence" and "Natural", were added. Infantile Pokémon in Diamond and Pearl, such as Roselia's pre-evolution Subomi, can be found in the wild, whereas in previous generations attaining one was made more difficult through the process of breeding. Baby Pokémon also hatch from their eggs at a lower level than in previous games. A crown is placed on Pachirisu in the Visual Judgement round.Pokémon Contests, events where one's Pokémon compete in a dog show of sorts to win ribbons, return from Pokémon Ruby and Sapphire as "Super Contests", with a few similarities and differences. Super Contests consist of three rounds. In the Visual Judgement round, players utilize the Nintendo DS's stylus to place accessories and objects on their Pokémon to appeal to a particular genre, such as "Cool" or "Cute", and earn points. In the Dance Judgement round, one's Pokémon competes with its opponents in a test of rhythm and balance. The final round, Performance Judgement, is identical in premise to the original; Pokémon use their techniques strategically to appeal to the judges and crowd. Assuming the same role as Pokéblocks, Pokébread can be made through use of the touchscreen and fed to Pokémon in order to increase certain traits and the likelihood of success in a Contest.
First introduced in Pokémon Gold and Silver, Pokémon Diamond and Pearl feature time, which is reflected in a number of facets, such as the overworld, in the availability of certain species of Pokémon depending on the time of day, and even the lighting during battles. The scale of the day and night cycle has grown substantially, featuring five different time periods: morning, day, afternoon, evening and night.
A new device called the Pokétchi, resembling a **** can be obtained and plays host to a variety of features, including a time management system, a calculator, a method for monitoring Pokémon in the breeding center, a type chart, a radar, a map, an itemfinder, a counter, a wireless link up seach, and drawing pad.
Below Shin'ou is an underground world, used for multiplayer gaming. Players can create and decorate "secret bases", like they could in Pokémon Ruby and Sapphire, and participate in minigames, one of which will allow the player to unearth fossilized Pokémon. Initially, only one fossil can be found in each game; the footprint fossil (new Pokémon Zugaidosu) in Diamond, and the Shield Fossil (Tatetopusu) in Pearl. However, after unlocking the National Dex it is also possible to find the Dome Fossil (Kabuto), the Root Fossil (Lileep), Helix Fossil (Omanyte), or the Claw Fossil (Anorith) in either version. 
The biggest addition to the series is the ability to go online via Wi-Fi and not only do battle against other trainers, but trade and collect Pokémon on a world-wide scale. There are several centers in each city that serve different purposes. One center allows the player to enter battles against other players, and join the Pokémon Union, a chat room of sorts where players may chat with people on their friends list. Another new feature is the GTS, or Global Trade Station. By entering the GTS forum, the player can search for a Pokémon and offer a trade. The trade does not have to be instant and can be left for other players to browse.
The developers have also added 42 new TMs, boosting the total amount to 92 (the Advance Generation games' fifty TMs are making a return). This marks the first time an entire 50-TM set has been left intact between generations. 2 of the HMs have also been changed, a former one of which has been downgrade
Diamond and Pearl are compatible with the Game Boy Advance Pokémon RPGs after earning the National Dex. The Pokémon Game Boy Advance cartridge is inserted into the GBA slot of the Nintendo DS, while the Diamond/Pearl copy is in to upload Pokémon. When you upload them, you go to an area called Pal Park and must capture them in the wild. Pokémon uploads are restricted to six per day per GBA cartridge, and the player will have to re-capture such transferred Pokémon in Pal Park before transfering from another GBA game. Also, you cannot transfer Pokémon from an English GBA game to a Japanese DS game.  The player cannot transfer any of the Pokémon back to the GBA cartridge once they are transferred to their Diamond/Pearl copy, as the transfer is permanent. The DS's native support for Wi-Fi is employed, allowing players to trade, battle and communicate through "voice chat" online. Diamond and Pearl feature Wi-Fi connectivity to the upcoming Wii Pokémon title Pokémon Battle Revolution. Diamond and Pearl feature a global trading system, which allows trainers to search for any Pokémon they want, the resulting list showing all the people that are willing to trade that Pokémon, as well as the Pokémon they want in return for it. Diamond and Pearl are heavy on version exclusives, Diamond has 20, as does Pearl. Every Pokémon is catchable without using Pal Park (except for legendary pokémon, Starter pokémon and said starter pokémon's evolutions).