Mario Party 8 is a fine entry in the series. Not one of the best, but it is at least fun in multiplayer with a few boards that are always fun to revisit. The minigames are a bit divisive among fans and I'm leaning more on the side that doesn't like them. So many of them feel a bit too ambitious for the base Wii remote which this was designed for. I imagine they would've been better executed with the Wii Motion Plus, but many of them feel more like fighting the controller than playing the minigame. Other than that, I'm not a huge fan of the "default realistic assets" look this game goes for, like Mario Party 4 did. The music is nice at least.
There are definitely worse Mario Party games out there, and it's easy to have a good time with this one, but it's not near the top of the list of ones I'd pick to play with friends.