I've done the North Sea 4 times in the last year, but via the Stenna Line, and have always found it totally fine and so did my friends - but people handle sea travel differently and with it traveling across further north this boat may be worse. If you're London or elsewhere, and you don't like flying, just take the Stenna Line from Harwich, get a train to Amsterdam and then book a hotel stay for 2-3 nights. It's a wonderful city and needs much more than a day to appreciate - less than a day would just be frustrating. It's a expensive city to eat drink and stay in though, so I suppose in terms of 'going for the sake of it' and it being cheap, I guess this is a good deal.
15% Quidco could track too.
Just park your car at Royal quays shopping centre in North Shields,it's only a few mins walk to the ferry terminal & it's free