Mario Party is not bad as a game. But it's like having a rabbit with that series--all of a sudden there's another, and another, and yet another! I couldn't believe it when I found out they were going to put out Mario Party 8 without Wi-Fi. They need to take more time with them and make them worth buying.
When my friends are over they're much more interested in Super Smash Bros. and Wii Sports or Mario Kart, so we just don't play Mario Party 4 anymore (we had some good times with it before). Even though Brawl and Mario Kart Wii will probably take most of the Wi-Fi time between us forum members, every once in a while we'll end up playing Mario Party.
I know Mario Party DS is going to have Wi-Fi play, but the mini games are probably going to be screen-scratching demons... I'll wait patiently for Mario Party 9 or 10. Let's hope it's not a half-baked attempt to make some money.
Note: I've only ever played Parties 2, 3 and 4, and I only own 4.