Some of our community members pride themselves with reviewing EVERY site they visit and I think for the UK there is no reason to do so, and in fact I'm not sure I want to review any of them unless I ever make it those uninhabited islands in the middle of nowhere...though I now pride myself with having reviewed ONE of the country's site (Bermuda is still an easy candidate that hasn't been added recently and IF you count it as being park of the UKas it is actually British overseas territory) and with Studley Royal Park it's also been years since the last review. Well, not that this place changes in ANY way.
The park itself is huge. It should be a day trip for the paid entrance alone. Not many people went to the free areas surrounding it. When visiting (or regularly?) they also had a sort of discovery game for kids which pleased the two young visitors that tagged along with me and made visiting every corner of the map worth it for them. The main interest of the visit should be Fountains Abbey which is grande and takes about half an hour by itself. The Gothic St. Mary's Church is much smaller and is more of a museum, and the rest is mainly just open garden areas. The strolls along the river and the lake are beautiful in summer and was totally worth the entrance ticket alone. We also arrived early in the morning and it wasn't crowded yet which helps a bit. I followed the red "recommended path" and exited at the west side of Studley Lake to enter the Deer Park. From there you can exit to the main road and follow a shaded path along back to the car park. Overall I spent maybe 5 hours in the park(s) but I would expect for the entrance fee, extra things to do (playground for kids, cafes) people will usually spend the entire day here.
So the question is if the site is unique in any way and in my opinion it is not. It's a worthy visit, definitely shouldn't be missed on your tour in the area. There just isn't really enough that gives me a "wow", it is after all more of a superlative version of an English park/garden that is well taken care of and combined with the abbey, church and the deer park.