I would change your directions slightly. It's not so much front to rear as it is top to bottom. The higher you are in the ship there is noticably more motion.
Basically, it's like this.
-The first night is always the worst as you will cross the Gulf Stream(yes the same one the weather guys all talk about). And under normal conditions, even it is usually not too bad.
- The rest of the cruise is usually very smooth- the ship has devices called stabilizers that help keep the ship running on an even keel, and the captain will go out of his way to find calmer waters, as far as changing the course entirely to run a smoother run.