They (Valve and Havok) haven't announced a left 4 Dead 4, but
they have announced a Left 4 Dead 3 coming out in 2011.
How do you get the passing on left 4 dead 1?
You can't get The Passing on Left 4 Dead 1. It is only a DLC for
Left 4 Dead 2.
Is left 4 dead a good game?
Left 4 Dead is quite a good game if you like shooting zombies in
an online mmo style. But, if you already have left 4 dead, you
should get left 4 dead 2.
Is left 4 dead fun?
If you love zombie games then you'll love Left 4 dead, they also
came out with Left 4 Dead 2.