I bought Pokemon Diamond to play on my DS earlier this year. I bought it because I was curious what made it so popular among young gamers and why it's a best seller.
As much as the game is easy to grasp, the challenge lies in attempting to collect every single Pokemon (a little less than 500 of them) and beating the many wandering and boss characters' Pokemon. Before I realized it, I had put about 30 hours into the game and still had a lot more things to do and monsters to catch and train.
I'll admit playing this on the bus or train, may cause one to become conscious of people looking especially when one is clearly "an adult". But who cares? I'm having so much fun.
Pokemon Diamond is at heart a strategy roleplaying game with a surprising bit of depth. Creatures have their affinities to different elements, and their moves may also be physical or elemental in nature. Some elements are strong or weak against elements. Therefore, in order to do well in battles, you need to select the right creature to do battle with your opponent. You need to select the best attack (you can four kinds of attacks or moves at any one time. When you learn new ones, you can opt to replace old moves or forgo the new move.)
You need to carry with you the right team of monsters since a battle can involve up to 6 pokemons, one versus one, one after another as the loser is replaced by another until one player or the other beats all his/her opponents monsters.
Like any rpg, the monsters gain experience for every battle won and you gain money to spend at in-game shops and such. The monsters can also be equipped with booster items and healing items such as fruits.
Some of the monsters are kinda cute. They aren't static though, after leveling up, you may get the option to evolve them for more powerful attacks or merely because you like a new and/or tougher look for them.
The game follows the NDS clock. So, if you are playing it during the day time, the game world is in day time; if you play it at night, the game world is in the night time with street lamps on and all. Some Pokemon can only be found at certain times of the day more often than others.
If the AI doesn't seem challenging enough, you can go head-to-head with real people connecting through to the internet or wifi.
Other than battles, there are also little mini-games scattered in the game world. Little pageants for your monsters, collecting more stuff and there is even this town with a casino. You can also grow fruit trees, then use the fruit for its healing type properties or cook them to boost monster happiness. (Monster happiness may affect their growth and how well they listen to you.)
I guess I am writing this article because I'm tired of seeing people dismissing this as a game just for children and missing out on good fun. No doubt it is made for kids but this is certainly an excellent game for all ages to enjoy.
Note: Pokemon Diamond and Pokemon Pearl are the same game: the only difference is which monsters you are given to start the game with.