I've noticed many peope complain about games in general for reasons like this, but I'll use WarioWare as my example.
First off, tons of you were complaining that it only takes a couple hours to beat. The game was not meant for single-player at all, the mode is mainly there to teach you the controlls and the general idea of the game.
In reality the game can be fun for many hours, doesn't quite stack-up to Mario Party but it's pretty close. Surprsingly there are a good few multi-player modes, although asides from a few new games they are all the same games switched around. But still, I don't see how 200+ mini-games with differnt game modes can get boring to fast.
Obviously most people saying it sucks are playing alone and vice-versa.
Again, party games arn't meant to be played alone! If you only play alone then don't buy them and then tell other people they suck! Just a little thing I've been noticing a lot.