Pokémon Platinum
The third game in the 4th generation of Pokémon, Pokémon Platinum is ofcourse very similar to its siblings, but also very different.
This game's mascot is Giratina, instead of Palkia or Dialga. And the outfits of the main characters has changed to accomodate the colder climate(you'll notice the spots of snow here and there in the game). The battle screen has changed to a darkgreen style instead of the usually white.
The Torn World; This area has two entrances, one ontop of Mt. Coronet and in the Turnback Cave. This area is most confusing and puzzling, so enter with caution.
The opening was also not left untouched, most of the new features were incorporated in the new intro. Most of the Gyms have had an update, Gardenia's gym per example has two huge rotating leaves that rotate when you defeat a trainer, you'll have to defeat all four if you want to progress to Gardenia.
The story has changed quite a bit too. Team Galactic is back, with a new member (a professor) who will later take an important role in the storyline. Giratina (as the boxart implies) will become more prominent in the story as it progresses on.
A lot of areas have had an update. The GTS Center in jublife has the WiFi Square now. The Resort Area now has the resort villa and so on. The Pokétch has had its update too, instead of one of the two colors blue/red it is now either silver and red or silver and blue.