As a sort of counter anecdote - we took a ferry from Portsmouth to Bilbao once, it was also just over 2 days on the sea. But oh boy, I regularly take ferries from UK to Netherlands, but I've never seen sea as rough as this. We were pretty much stuck in the cabin, sea sick, for the entire two days. I decided to brave the neausea and attempt to go for some food, but in the main buffet plates were literally sliding off the tables.

On the way back we decided to drive through france and skip the ferry.

But yes, on the Newcastle to Amsterdam crossing my favourite thing is being completely cut off from the internet, can finally sit down with a book without the compulsive need to check my phone every 5 minutes.