They were/are awful. GM knew the PCV system was undersized from the factory, as well.

 

The LNF has a second line attached to the valve cover, goes from the back of the valve cover to the inlet of the turbo. The line with the valve, it's more like a metering valve than a check valve. GM designed it to control the amount of fresh air incoming to the valve cover. Air goes into the valve cover there, vacuum is created by the other line (closer to the timing chain) to the turbo.

I forget how the PCV in the intake manifold is connected into the system, I might have it written down in some notes somewhere (but I'm lazy and not looking for them).