Variety of fun.
I like the variety in the DS Mario Party; story mode, board game mode or just jump into a head to head mini game which there are 70 plus.
My girlfriend and I play just off my single cartridge in my DS and download the second player into hers and there is nothing lost in gameplay.
Playing alone is fine but there is more satisfaction and competition in playing against someone who sitting across from you. The only fault I can truly find with this game is that there isn't any wi-fi play.
The games are involved whether it have you blowing into the microphone to knock over a Whomp or spinning the stylus to throw cherries. I have to say that I looked a little foolish playing this at my local cafe and blowing like a mad man into the microphone in the public.
I highly suggest this game for two or more players but if you are looking to pass time while waiting then single player will suit just fine.