Much as I love the Harwich to Hook of Holland crossing, Harwich terminal is awful (and the cracked A120 leading up to it isn't much better), and in stark contrast to the one at the Dutch end. I know the ferry services have severely dwindled, and foot/rail traffic in particular, but it's a particular, dated, concrete ghost town of a place. And, if you're catching the Cambridge-bound boat train, you're in for quite a wait there...
There's also the question of how you cross the railway when going from the A120 to the ferry. It's a rather inelegant solution. Rather than the access road going over a wide access bridge further upstream, traffic is segregated. Light traffic goes through a slightly terrifying, narrow concrete spiral overbridge (including pushbikes - great fun climbing that slope with a transit van up your backside) whereas HGVs filter through a level crossing.
If I can have a word for one entirely outside the UK, though: Malmo. I've often been the only ferry passenger there. The ferry "terminal" (an oversize portakabin) isn't accessible by foot, so you're basically stuck inside until they either send a port minibus to drive you on board the ship, or a taxi into the city (and you'd better hope the taxi turns up). This is the unregenerated harbour in Malmo, too, so it's a mix of heavy industry, Ro-Ro traffic and industrial decay. OK, barely worth their while building anything more substantial, but it's still a hell of a place to be stuck.
(It's frustrating on the other end too, in Travemunde. Lovely big, new terminal building which, again, you get shuttled to by port minibus. What's frustrating is that there's a railway station, been there for donkey's years, NAMED AFTER THE TERMINAL, which you can see, but can't get to any more. You have to get a rather infrequent bus, which you often miss because the port minibus only comes when the car deck is empty. Hey-ho.)