While the mini games are interesting, lazy luck based play destroys the fun and no team mode ruins parties.
First thing I noticed was that my wife and I can't play on the same team in party mode. We have to play against each other and there's a huge lack of team work based games. This is very annoying to not even have the option.
Secondly, we discovered that everyone moves together. So the game removes most of the strategy to special dice blocks by forcing you just just play the "roll a number, have no choice, land on a spot and do what it says" game rather than mixing and matching dice to play strategically different from the other players.
Thirdly, the party games quickly devolved into each player trying their best to not fail rather than to succeed. Every other space is a penalty to take away your stars, each map has an annoying "lose half your stars" mechanic that happens multiple times in a game and can't be turned off. It's annoying that the main mechanic in the game is punishment based rather than reward based and it is in no way fair, it's simply random.
Fourth, the party version and the mini-games have been really dumbed down. In MP8 you had candy that could do all kinds of cool stuff and gave you lots of options to overcome bad luck. In MP9 it's a "roll your dice...move your mice and may lady luck shine on you" game. There's little to no thought, no planning, no strategy and thus it's very boring.
Fifth, because the game is so luck based, there really is very little reason to try and win mini games. I can play 4 player mode, win every mini game, and lose by 30 - 40 on a regular basis because it's all just luck, luck, luck. Give stars to last place, lose half your stars, play for half your stars, etc. Why? Balance your game and stop using lazy mechanics if you have to use forced luck.
Sixth, the bonus stars at the end of party mode are generally useless because 90% of the time the winner is leading by more than 15 stars. So even if you somehow manage to win all the stars it still does no good. In MP 8, you didn't win by 20 or 30, you won by 2 or 3. So the 3 bonus stars at the end might actually make a difference.
Conclusion: It's ok to play with real people because you can kind of create unofficial teams, or try and remove luck from the game as much as you can. The mini games are ok in stand alone format because there is actually some skill involved (very little) and less luck. But party mode, and single player mode are worthless with single player mode being the biggest monotonous pain.
With real people, it's a decent enough party game for mini games, but it's not worth spending much money on and you'll never play it in single player mode more than once. It's easily the weakest Mario Party game yet.