Good at what it does.
If you're looking for a pokemon with a good plot, this is the game for you. Being someone who's used to the pokemon series having little more then an excuse plot I'm surprised finding that the PMD series and EOSky to have a decent plot. Well I won't go into details, it may catch you by surprise how deep and emotional is if you can get past the contrived stupidity of the characters (at times). The only issue with the plot is it has more then a half dozen moments where you do something stupid and cannot do anything about it (Though it is a common JRPG problem, so I'll let it slide), however there are a few moments where the plotline can also make you cry (Or so I am told).
The music for the game is pretty superb, several of the music I keep on my MP3 encase I wish to listen to them. Which all things considered it's pretty good, most of the regular pokemon games nail the 'battle themes' but are completely lacking in most BMG's for the areas. Now not all of the themes are good, but there are many that are, and for a pokemon that's quite good.
The Bad:
It's Mystery dungeon.
Yes that relic is still being used in games, where if there was some actual effort put into it, it could be something much more likable the developers seem to have phoned it in when it comes to the dungeons. Most of the dungeons have only 3 different tiles for the ground, the walls, and the 'thick' walls. Which 3 is not varied enough to make it look anything more then a lazy C&P job.
All of the dungeons essentially are the same bar greater complexity (See: Smaller rooms and more corridors) and having pokemon appear that match the dungeon's 'theme'. Let's also not get into the problem of how the dungeons and the pokemon mechanics do not always agree.
Conclusion: So you may be thinking, if the dungeons (The core of the gameplay) are so bad then why are you giving it a 9? Well that's for two reasons. First off, I never went into the second PMD game expecting good gameplay, but I was expecting an even better story; So it met all my expectations and more. Second off, if you think about it, it has better combat then most of the normal pokemon games which can be described best as a "Paralyzed backing and fourthing of blows, like some sort of bizarre televised debate" this actually gives you a whole two dimensions that you need to consider instead of the whole one dimension in the normal games.