If you've got 3 friends and this game, you're going to have one heck of a party.
However, Mario Party DS (MPDS) changes this formula by using the Nintendo DS. While the single player is rather lame (like all mario party games), when you have 3 friends with DS's, this game is so much fun.
One Game Card, 4 players. The ENTIRE game is able to be played as DS Download mode, which is amazing. The load times are pretty fast too, once you get past the initial download. I used to play this on the bus for about 30 minutes back and forth when I was in High School.
Some of the MiniGames are super lame... but thats in all Mario Party games. Many though, are a blast with 4 players. One of them has you playing Hot Potato with a huge dynamite (wick) bomb, and you blow into the mic to have the fuse go down. You have about 5 seconds on your turn, then it goes to the next. If you blow in the mic, it goes faster, but if you are quiet, it goes slowly (so you can avoid it blowing up on you). This is insanely fun, but unfortunately the way the DS Lite's (no idea of DSi) build is, it always senses sound in the hinge and you end up killing yourself quite often.
The game also does a number on your touch screen, but when having this much fun you don't really think about that. There is a good variety of mini games, so you won't get bored too fast, but they do get repetitive, but not too much that it gets boring.
If you have a family or some friends with DS's, you should get this game. If you are only going to play alone, this is a rental. It's fun, but only for the multiplayer.
I give it 8.5/10 for multiplayer, but if it was only single player, I'd have to give it a 5/10.