The first time I rode Amtrak, I was quite surprised at how much fun it was. Seating is very comfortable and if you need extra space, the lower level is great. It was really nice to be able to sit back, relax, and just enjoy watching the world go by without having to deal with traffic. The rates are very reasonable. If you need something to eat, there is a small snack bar available on one of the middle cars. I recommend bringing your own food, though, since the prices are a bit on the high side.
The bathrooms aren't great, but at least you don't have to pull off the road and find a gas station where you have no idea what you might be walking into.