Just picking up this general thread about rail-boat connections.
I used the Harwich-HvH link (overnight) recently, for the first time in many years. It remains - largely - an example of how such connections can be good. The station/port link on the British side was integrated and under cover, a short distance and quite quick (and less grotty than I remember it used to be...) And on the overnight crossing, where you have a cabin reserved anyway and aren't worried about finding a decent spot for the crossing, you can catch a train arriving not long before check-in closes (ie later than the scheduled "boat train"), so as to avoid much time wasted, faffing around queuing for a queue. [NB - I guess someone here knows whether there are official connection times for such things, like for connections between trains in Britain, so that if a nominally appropriate train is delayed and you miss the boat, you don't lose out on your onward ticket just because you're on a train later than the through boat train they show on the boat timetable?]
On the Dutch side, I was surprised about the walkway from the gangplank to the passport control and the railway station: nice and bright, and no steps, and a travelator for a bit of it, but ...it must have been about a mile long! Integrated, yes, but quick and easy, no. Does it depend on which bit of the quay the boat docks at? Do some boats have their exit nearer the landward end? Is it always that long a hike these days? (However, on balance I'd much rather this than going "outside" to get a shuttle bus a few minutes across the port, as in some places; the feeling of an integrated connection is, I think, important in terms of the image of rail-boat links being as convenient as rail-rail connections.)
And of course the new metro is fine (though as a metro-style service, I'd have hoped for better than a half-hour frequency on a Saturday), but having proper trains back there would be better. Maybe, as surface transport comes back into climate-needed fashion, that will change again one day soon. But overall a fairly smooth and fairly cost-effective journey from London to the other side of the Netherlands. I'd certainly consider that route instead of Eurostar again sometime, depending on where I'm trying to end up on the other side, apart from one problem - see below.
As for the boat itself - perfectly comfortable and mostly efficient (though information telling foot passengers where and when to exit the boat was a bit iffy), And the cabin was excellent. Given the through ticket price from London to anywhere in the Netherlands, then the comfortable night's sleep for very little compared to a hotel price was good value. Given the distance covered, and the quality of the accommodation, it was better value than many rail sleeper services.
One really major grouse though. Having got up bright and early on the way to HvH (even despite the clock change), so as to enjoy a proper breakfast before we docked - to set me up for the several train rides ahead - I was horrified by the loud "background" [in fact, foreground] music being played in the only place you could get a proper breakfast (as opposed to a cup of coffee and a croissant). It was so dreadful to be aurally assaulted in that way first thing in the morning that I couldn't cope and ended up with no breakfast. For that reason alone, I'm reluctant to use the overnight crossing again. It was the one thing that stopped it from being a pleasant and civilised experience.