Currently, you get two stories. Dark Dreams and Wet Dreams. 3.0 will get us more and I believe the current stories might be getting extended.
As for how many hours of gameplay, no game can tell you that. That will depend on the player. You might play it once, figure that's enough and never touch it again. Or you might find the story enjoyable enough to keep playing several times. Or you might simply enjoy the sex and use the Fast Sex option after playing through the first time. Or, you might enjoy playing around with things and messing around with the physics.
I vary between the three.

I've said this before in other posts, but I feel that the price is well worth it. And when 3.0 does come out, you only pay the small upgrade fee and get even more content. And it'll be a new experience as well since 3.0 will be running on a new and better engine.