A refreshing new idea to the worn-out Mario Party series, but so full of problems it's hardly enjoyable.
The single-player story is cliche and full of holes. Your selected character is watching some "mini-stars" in the sky with the rest of the crew, when Bowser suddenly steals them for undisclosed reasons. You then follow to recover these, and, according to the storyline, get back every last one, even though it's impossible to get them all in any stage. You have to recover them while riding a car with Bowser's minions, because you can't just stomp them on the face like Mario characters usually do.
The fun part is how the game parodies its and the typical Mario game's storyline. At the start of every stage, Bowser Jr. tells Bowser you have proceeded, and then Bowser prepares... to call some minions. This little narrative is done very well, although it's sadly the only story segment in the game.
Gameplay 1/10
That's where the game failed. It's nice that they tried to innovate, but everything is just plain bad.
To make things clear, you play along with all the other characters in a car. Each turn means a character's turn to move the vehicle, and everybody else moves together. There are various events triggered on the board, some giving the "captain", the one who controls the car on that turn, advantages, some bringing the good ol' mini-games into play (they don't happen automatically), or disadvantages like the Bowser space. The goal is to cross the stage, collecting the various mini-stars scattered on the stage and rewarded in mini-games and defeating the boss along the way. Note that the boss is fought in group. They usually just sit there doing nothing waiting to be defeated (it's impossible to be defeated by a boss).
Now to the actual review. The game offers extreme instability. Everything can change depending on your luck in a single dice roll. While other Mario Party games did rely on luck, it was done modestly. There were little advantages and disadvantages, complying with the law of large numbers, and the minigames offered rewards to the skilled. But in Mario Party 9, minigames rewards are meaningless. It is common to get the triple of the advantage you'd get in a minigame through a single dice roll.
To make matters worse, thanks to the car system, there is no "game" to "play" outside of minigames, which are rarely triggered. All you can do is roll the dice, wait, roll, wait, roll. You can't buy special dices, only get them through luck. If you get a wrong roll, you can lose half of your mini-stars, and that's not even rare.
On another topic, there are very few game options and conditions. You can only play the single-player mode, party mode, or extras (read: perspective mode; 20 minigames with a more difficult camera view). Since you just have to get to the end of the board, everything is unusually short. The single-player mode can be beaten in one sitting, if you don't constantly lose due to last minute lucky turnarounds. The multiplayer mode has no internet support. If you want to call some friends over just to play this, it could be fun, but be warned that MP9 is so much luck based you'll probably just get in a fight, and so short you should have another game to play once you've finished this one.
The perspective mode is short, and only fun for the first 5 or so minigames, meaning 10 or so minutes. The rest is a bunch of fake difficulty thrown around by making you unable to see your surroundings.
There is a shop in the game just like in MP8, but it hardly encourages anything. The only useful thing that can be bought is a single new stage, the rest is purely aesthetic, ranging from new vehicles to pointless constellations.
Graphics 9/10
The only good part of this junk. The graphics are technically wonderful, as you would expect from a game developed in the Wii's late stage. Smooth models, great textures, and various animations. The interface isn't awesome, but it isn't terrible, either. Not much else to say in that regard.
Sound 2/10
When the game isn't completely silent it is playing the same tracks over and over. These tracks are mostly 10-second loops, not a prime masterpiece.
And there are the sound effects. Most actions are done silently.
Almost every sound effect that IS there would have worked correctly if it was not ruined by the constant silence. Some, however, are extremely flashy and annoying: losing in perspective mode, Toad's constant "WOW! YAY!", etc.