Ideally, every game should have strong single-player, strong local multi-player, and strong online multi-player.
And yes, games like Mario Party 8 with almost no reasonable single-player is just as bad as ones like Shadowrun or Warhawk (which at least is just a cheap downloadable). Motorstorm is a rip too with no local multi-player and limited single-player, but at least they know it and are adding play modes.
Personally I think devs are spending so much time optimizing graphics in next-gen titles that a lot of other stuff is getting left out.