Over in the OT, I linked to my previous post in another thread with some impressions, and some other players left their own impressions in the OT as well.
To summarize what I'm feeling (as a veteran of the AC series and someone who really has no context playing Mario Party games), the game isn't necessarily "bad", which I would judge by being unplayable due to bugs, glitches in general or just piss poor mechanics.
The game is just....it's boring. The Board Game mode you're forced into and I completely skipped over some of the other options to lower the gameplay time so I ended up dumping an hour and 15 minutes into it. Then it sends you back to the plaza but you're forced to play another round...this is before you even get to see that there's more than just the one game!
And then after you're done and spent all this time, the game shows you a bunch of different modes, but guess what, you gotta unlock them! Nothing that I played outside of a few modes were really entertaining enough for me to continue to grind on them to unlock the other modes which should have just been available from the start.
If you wanted to rationalize your purchase, I'd say you're paying about $31 for a handful of minigames that are kind of ok maybe if you're playing with friends. ($13 for Isabelle, $13 for Digby and $3 for the cards). As a single player, I think you'll find other games worth the money elsewhere. If you have friends or people you'll be playing with, it might be worth it.