If you want a party game, you quite simply can't do better than Mario Party 3.
The game starts with Mario and friends being disrupted by a falling star, which happens to be the Millenium Star, a star born every thousand years. Then, they get sucked into a toy box, where they are greeted by the millenium star, who tells them that they have to claim seven stamps in order to be called the "Millenium Star."
There are two basic modes, story mode and party mode. Story mode is self-explanatory. You go through a set number of maps and come in first each time, or you can start it over and beat it. Party mode is a free mode where you can do anything at anytime, from playing minigames in the minigame room to playing the board games there are. There are two types of maps: party and duel. In party, it's another Mario Party game. Four characters battle it out on a large map and try to collect stars, which are sold for twenty coins. While it may seem as repetitive as the rest of the series at first glance, and it seems as though chance is still a strong factor, each map has its own unique challenge and doesn't lean too heavily on chance like the rest of the series. Duel mode involves only two players playing to beat the other player with sidekicks, which are guys that go with your character of choice. Each partner has its own abilities and weakness, and can attack or defend. Your character and his/her sidekicks have a certain number of heart points. The object of the game is to deplete the other players heart points to zero by attacking them directly.
Graphically, the game is actually the best in the series due to the fact that Hudsons effort level has dropped quite a bit. The game may look aged, but the graphics are better than Mario Party 8, the newest installment. For MP8, that's inexcusable, but the fact remains that N64 had better graphics in its day than what is made out of it. It also sounds very good. The board theme music for each board sounds very nice and while the sound isn't among the greatest in video game history, it certainly holds its own against other titles of its era or even perhaps today.
When you add everything up, Mario Party 3 is the best in the series. While it may seem like another entry into the series, it is in fact a better experience than the rest of the series. If you can find a copy, then by all means get it. You'll most likely enjoy it.