Once upon a time, Pokemon was a great handheld role-playing game. As it turned into an anime, a collectible card game, and merchandising opportunity galore, the original game was forgotten... overshadowed by mountains of happy meal toys and drowned out by the incessant sounds of "pika-pika!" emanating from televisions across the world.
For the three of you who didn't actually know that Pokemon started out as a game, the original premise is quite simple. Starting out with one pocket monster (chosen out of three), you battle your way through the world by catching new monsters in the wild, leveling up your team, and generally using cute creatures to do your dirty work. The system's depth comes in when you add that each monster is assigned a "type," be it bug, fire, ghost, or any number of others. While most RPG's have similar sorts of rock-paper-scissors elements (light beats dark, bows kill things that fly... that sort of thing), creating the perfect team with the over 15 types of pokemon almost requires calculus. To make things even more involved, monsters can have more than one type, leading to double weaknesses and resistances. An example: the pokemon Sableye is a Dark/Ghost combo type that has no weaknesses (for now) because Dark-types resist the weaknesses of Ghost-types and vice-versa.
All of this "type" interaction seems like a chore on paper, but the practical result is addictive and fun. Putting together a team you like is extremely satisfying, and there's always a new creature waiting for you in the next area that just might make you even more unstoppable.
Diamond and Pearl look to take this well-established formula and very carefully augment it into a worthy next-gen title. While the sound effects, battle animations, and general adventure design will seem very similar to veterans of the current games, Diamond and Pearl add a very welcome level of polish to the interface with the inclusion of touch-screen controls. The game world will, unfortunately, remain strongly grid-based, with the same top-down view used in the previous games somewhat bolstered with some 3D elements. The day/night cycle will be upgraded to 5 different times of day, and the "backpack" items see an upgrade to match the new features, including a pokedex that is touch-screen controllable.
These little upgrades are really nothing more than icing on the cake, because there's really only two new features you should be excited about. First, that there will be a large number of new pokemon to catch, including new evolutions for current creatures. Second, Diamond and Pearl allow players to trade and battle over Nintendo WiFi, finally making the multiplayer aspect available to those of us who don't have a group of pokemon-playing friends. These new online interactions will even give you the opportunity to voice-chat using the DS microphone, a feature currently only available in Metroid Prime: Hunters.
With the Japanese version already breaking sales records, think of Pokemon Diamond and Pearl as Nintendo's way of atoning for their over-marketing sins. The formula hasn't changed much over the years, but it never really needed fixing. There are more monsters to catch, more trainers to fight, and wi-fi support that will finally allow trading and battling with people besides your local friends and that weird pokemon guy who hangs out at the mall.
April 22nd can't come soon enough.