If there's one thing you should take away here: It's that you need to play this game. Immediately.
But, if you found this review, and this game, please. Stop reading this review and go buy it. It's an odd thing to say, but go. Now.
Just go.
NOW.
DO IT.
Alright, fine, Mr. Stubborn. I'll tell you why you should go buy it.
Gameplay: I don't know if you've ever played a roguelike, or heck, even know what a roguelike is, but essentially, it means you go through "dungeons", climbing from floor to floor in randomly generated maps, fighting enemies and getting loot. All the dungeons are randomly generated, which means you're never going to go through the same place twice.
However, this is a major takeaway from the game. The dungeons themselves aren't really that interesting, they lack dynamic, more interesting enemies, traps don't appear until late, they are often insanely long and get tedious, and there isn't really anything to break them up. Add this to the boring dungeon generator, which places flat square rooms divided by massive corridors and the occasional dead end, and the gameplay isn't very interesting to start with.
The addition of Pokemon into this formula does help it a good deal, however. You can encounter almost every single Pokemon from the main series, all with their unique attacks, which does help to liven the combat. I just wish that the dungeons had more of a variety of Pokemon in them, most dungeons have 3 or 4 different Pokemon that spawn in it, tops.
To add to your "team" of Pokemon with which to tackle these dungeons, you must "recruit them. This randomly happens upon defeating an enemy. The system leaves a lot to be desired, but it works well enough, for the main storyline anyways.
But just exploring random dungeons doesn't sound very interesting, especially when the dungeons aren't. You can take side missions and bounty hunts in these dungeons, which appear on certain floors. It helps to liven up the action a bit.
For your obligatory RPG item needs, there's also a small town where you can do things such as store money, buy items, store items, train, the usual RPG stuff. There's also a few other interesting shops, like one that allows you to increase your abilities by drinking...gummis apparently. (No, that's not a typo).
Graphics: In terms of graphics, the game is a mixed bag. The animations on the Pokemon themselves are miminalistic, with very simple leaps and steps. They are quite colorful and lively, and they often contrast well with their backgrounds, which can look pretty at times.
Outside of dungeons, the game looks okay, even nice once in a while. It's certainly not going to raise any eyebrows, but the colorful world does have a certain charm to it.
Inside of dungeons, the graphics are a nightmare. They're ugly, repetitive, and bland. You'll see the same dungeon wall over and over again, and it's not really well drawn. Dungeons aren't realistic, they're just simple boxes copy pasted with tunnels connecting them, which looks astoundingly boring. There's about 2 or 3 floor tiles per dungeon, which is really pathetic.
Sounds: The sounds of this game are also a mixed bag. The actual attack sound effects, item pickups, and really anything that isn't the music sounds outdated and boring. It's enough to not take you out of the game, but it certainly doesn't add anything to it, and it just feels boring.
The music, however, is oddly enough quite well done. I found myself actually listening to some of the songs outside the game, which is surprising. Some dungeons have music that simply tries to recreate the feel of the dungeon, like the Northern Desert, others try (and succeed) to convey the emotions you are supposed to feel at the time in the plot. Especially as the game goes on, the music only gets better and better, with some of the final soundtracks some of the best music I've ever heard come out of a DS game.
Story: The story in Pokemon Mystery Dungeon, in a stark contrast to the rest of the Pokemon franchise, is literally, the reason to play the game. It starts off pretty slow, and characters have an annoying tendency to repeat everything a million times before moving onto a new subject. "Hey, did you hear the sky is blue? Yeah, really, it's blue. I really can't believe it's blue. That sky really looks blue. Yep, it's totally blue." Maybe it's a problem with the translation to English, but then it's just a poor translation.
However, as the game goes on, the story really starts to pick up. At first it gets somewhat interesting, then really interesting, and it really starts to go from there. I really don't even want to spoil a minute of the story for you, I won't even tell how it starts. Let's just say that it's a story that needs to be experienced, and the ending of this story is the high note, having one of the most...satisfying endings ever.
It also helps that the music compliments the story so extremely well, especially the later songs.
In closing, Pokemon Mystery Dungeon, as a game, fails. It's so plainly average, there wouldn't be any reason to play it. However, it does one thing right. It uses it's existence as a videogame to tell a story, involve you in a story, and in reflection, it's the best example of how to use videogames' uniqueness in the entertainment media to tell it. It's the only reason to play the game, but it's such a damn good one it doesn't matter.
It's sad however, intended for such a small market, an even smaller number of that market will actually see it through. Ultimately, it's the incredibly rare gem that few will actually see, but those who do will find the most unique and incredible video game experience of their life.