Pokemon Platinum is the sequel to the first 4th Generation games called Pokemon Pearl and Pokemon Diamond. Platinum stars a new legendary Pokemon called Giratina. This game features several new features that were not in Pokemon D/P.

• Gardenia's, Maylene's, and Fantina's, gym have been redesigned.
• The Elite 4 have their rooms redesigned.
• Teams of many trainers including the E4 and Gym Leaders have been changed.
• The Battle Frontier now includes the Battle Castle, Battle Hall, Battle Arcade, and the Battle Factory
• Rotom, Giratina, and Shaymin were introduced with new forms
• There are 2 new key characters which are Looker and Charon
• You may own your own house in the Resort area
• There are new Wi-fi features
• Some main characters you battle will have an animation when you enter a battle

There are many more to list but I think you can find them out yourself.

The game starts of with a TV Screen. When it fades out, you find yourself in front of your tv at your house in Twinleaf Town. You go down the stairs and your mom tells you that your friend needs you. Do all of that and eventually, you go to the route above Twinleaf Town with your friend. A Professor and his assistant come up to you. Go through the conversation and then you are offered a Pokemon along with your friend. You have a selection of the Fire Type Chimchar, the Grass Type Turtwig, or the Water Type Piplup. After you choose a Pokemon, you will have some more talking with the professor and then they will leave for Sandgem Town.

Right after they leave, you a challenged to a battle with your rival.

The story continues on and you will go on a quest to conquer the Pokemon league. You defeat Gym Leaders, face a threatening team called Team Galactic , meet many Pokemon, and do other things. Catch and raise your Pokemon along the way. Will you be strong enough to defeat the Champion?