I've not been there, but I suspect Marineland at Antibes (France) would be a closer match; not least because they have Killer Whales (only Antibes and Loro Parque have them in Europe currently).
Harderwijk is certainly North-west Europe's closest equivalent though (in fact it represented the closest captive cetaceans to my home until it sent two porpoises to Ecomare - and still remains the most 'accessible'), and very much a marine mammal specialist collection. They have seven marine mammal species on show - Atlantic Bottle-nosed Dolphin, Harbour Porpoise, Pacific Walrus, Steller's Sea Lion, California Sea Lion, Common Seal and Grey Seal - and a small-but-currently-being-expanded North Atlantic fish display. They do not have penguins, turtles, Polar Bears etc (though to be honest it's rather surprising they don't at least have penguins!).
They do exceptional work in cetacean rescue and rehabilitation on site, and did in fact have a single (rescued) Killer Whale recently on show, though it has now moved to Loro Parque.
