I think there should be more games with either JUST multiplayer or JUST single-player - so that the developer can spend their time making the game so completely badass it blows your skull off, instead of two mediocre modes. The only example of a game I have played that balances that well (it's not badass, just fun) was Halo 3, which is pretty much a staple of friendly parties, and if you look back in hindsight, the campaign is ridiculously fun. I've been playing COD4, 5, TF2, and Bioshock for a very long time, so I'm a bit rusty, and it's still as fun as it was when I first got it.
And before you start spouting your vehement statements: There are TONS of games I have not had the pleasure to play. I am a "new" gamer. PC at 1999, 360 when it came out.