Note: Since the core mechanics of the game remain the same from previous iterations, I've based this review on them. New features specific to this iteration are in italics.
Pokémon Platinum is from the 4th generation Pokémon games, which is an improved version of the Diamond and Pearl games. The typical Pokémon gameplay remains the same. You start out with one Pokémon and travel the world, catching more Pokémon, training them up, and battling your way to beat the Elite Four; the best trainers around. Your secondary aim is to collect them all, but this is normally only possible by owning other versions, then trading between them. In this version, there's the ability to interact over the internet, but Nintendo Wi-Fi Connection was discontinued in 2014.
Pokémon are found in long grass, caves and water and are encountered randomly. The various species are found in certain areas of the world and have different rarity. The day and night feature from the 2nd generation is back, which means different Pokémon can be found at night-time, which gives you the incentive to revisit previous areas at a different time in hope of catching some nocturnal Pokémon. Another 106 species have been added though making a whopping sum of 493 creatures. The new species are generally good, but there's a few embarrassments.
Once you enter a battle with a wild Pokémon, you engage in a one-on-one fight. Knocking out your opponent gives your creature experience points, or you can choose to capture them to add them to your collection. You do so by throwing a Pokéball which has a random element to your success. Your chances also increase the weaker the Pokémon is, and if it is inflicted with a status (such as Asleep or Paralysed). You can only carry six Pokémon at all times, so exceeding this limit automatically transfers them to your PC storage facility. There's a few areas where you team up with a non-playable character who partners you in a 2 versus 2 battle against wild Pokémon or other trainers.
There are plenty of rival trainers to battle over the course of the game. Defeating them gives you more experience points compared to battling wild Pokémon. Additionally, they give you a cash reward which is used to purchase Pokéballs and healing items from the Marts. Double battles make a return and now your opponents have back-up Pokémon, although it's usually unbalanced. For example, one player may have 3 Pokémon but the other player only has 1. Therefore if you take out the player with 1, you are left on a 2 versus 1 battle. It would make sense for that player to send one of his reserve Pokémon to keep it at a 2 versus 2. These battles can also end quicker since some moves (such as Surf) can attack two Pokémon at once, and there's even some moves like Earthquake that will hurt your own too.
Your Pokémon fall under different categories which modify their strengths and weaknesses. This follows a rock-paper-scissors mechanic e.g. Water beats Fire, Fire beats Grass, Grass beats Water etc. The amount of types in the game, and the fact a Pokémon can be classified under multiple types mean the strategy is much more complex than this.
The 'ability' and 'nature' features which were introduced in the previous generation remain. Pokémon's abilities can can an extra dimension to the battles like Starly have 'Intimidate' which reduces their opponent's attack power when the battle begins. The nature modifies their attributes as they level up. For example a 'Hasty' nature increases speed but lowers defence, whereas 'Naughty' increases attack but lowers special defence.
The moves that a Pokémon learns varies by species. Each move has a type, attack power, accuracy, usage limit, and can have other properties like being able to poison, paralyse, sleep, confuse, burn, freeze and more. Your Pokémon gain more moves as you level them up, but can only know four at a time, so moves must be forgotten. You can also teach your Pokémon moves that can't be gained by levelling up, using items known as TM and HM (technical machines/hidden machines).
There are other types of items available which can heal them or boosts their statistics. You can go to the Pokémon Centre to fully heal your roster for free of charge. If all your roster are defeated, you are sent back to the Centre but with a financial penalty.
You can choose to be a boy or a girl. The other character is then introduced as another wannabe Pokémon Master and becomes a friendly rival. In addition to your quest to become the best Trainer, the story revolves around Team Galactic who plan to unlock an alternate dimension.
The graphics have been enhanced to meet the power of the DS. There's some user interface tweaks to allow you to battle using the touch-screen, selecting the large buttons by touch. The sprites are animated when they are introduced in the battle, and many battle animations have been updated.
The berry system remains similar to the previous game. You can now plant berries in soil and come back later to collect them. There's essentially two types of berries. One are hold items which your Pokémon can automatically use mid-battle which heal health or cure status effects. The other type can be used to create Poffins (formerly Pokéblocks). These can be fed to your Pokémon to boost a separate set of stats that are used in Pokémon Contests. In these contests, you show an audience your moves over a set of rounds with the aim of impressing them. This time there's some extra elements like an interactive rhythm and fashion mini-games. It's not exactly exciting, but it's an elaboration on the concept.
The Pokégear has been replaced by a Pokéwatch. This stays on the lower screen outside of battle. As you meet certain characters, they give you new apps to cycle through on your watch. The graphics are LCD style, so are pixelated and are simple in functionality. There is a watch that shows you the time, an app that shows you the level of your Pokémon in the daycare, an Item-finder, and many more.
If you find a flashing TV, you can read the subtitles of the show. If you have transferred data to your friend's game, you may get a show about a battle they engaged in, or details of their extravagant bulk purchases in the Marts. It's a simple idea but puts a smile on your face. The secret base mechanic has been moved to a Wi-Fi connectivity mode in the Underground. This is where you can create a base which you can decorate with all kinds of furniture.
Once you have beaten the Elite Four, you gain access to a new island where Pokémon from the previous generations reside. If you like the collection side of the game, then you can get many hours running around the island and visiting the new areas. There's also a few legendary Pokémon to catch at this point. If you own Pokémon Ruby/Sapphire/Emerald, you can pop the game into your GBA slot on your DS and transfer Pokémon. Instead of a direct transfer, you can transfer 6 per day, which then appear in the Pal Park for you to then re-catch. All the fun is taken out of catching them though, you just select to throw a ball and are guaranteed to catch them; so it's just a cumbersome and pointless system.
In this iteration, I found the battles to be easy. Usually, it takes a while to get going, and you have to rely on status changing moves like Confuse Ray and Thunder Wave to give you the edge in battle. This time, I didn't find any Pokémon that had these moves until late in the game where they aren't as useful. I also found the gym leaders and Elite Four to be easy, although the Champion proved a tougher battle. There's usually a few puzzles that appear challenging when you first tackle them, but this also seems missing from the game.
Pokémon Platinum is the same old game really. There are new Pokémon to discover and some tweaks here and there. The series is becoming longer and longer with each iteration which can add to the repetitiveness and it starts to become tedious. If you like the series and still have the passion for it, then you will probably enjoy it. Without dramatically changing the mechanics though, it's a series that is becoming stale.