My son had a day off from school so I took the day off from work and got us tickets to the Intrepid so he wasn't home all day staring at a screen. I never take the ferry across the river because the train or the tunnel (if driving) are much more convenient and cheaper. The downtown stop is a better stop closer to the action but the midtown stop is only good if you are going to Javitz or the Intrepid.
The cost is too much, the journey is on a less frequent schedule than the train and the parking at Port Imperial is also too much.
So yeah, if this is your first time or if you are a local showing someone the city, this is a nice journey. If you want in and out quickly, take a train.