I'm yet to have the 'wow' moment from any recommendation service.... Netflix, Amazon, Deliveroo... At best I get the 'meh why not'. It's obviously a hard problem to solve.
What about Youtube? Im surprised to not see them mentioned in any of the comments under yours. For all their faults, I regularly am recommended amazing(ly interesting to me) videos.
I read that something like 60 hours of video are uploaded to YouTube every second, so I find it hard to believe that the best stuff they can recommend is the same handful of 9 year old videos I've already watched sprinkled with dogshit right wing American political content.
My view on this is that recommendation services are made to try to funnel people to the same thing. While they sell some kind of "hyper personalization", they're just another kind of classic marketing. Especially for Netflix. Talking about series you watched seems to be a big part of watching series, so pushing people to watch the same stuff works better.
Or maybe that is not the problem they are trying to solve. They optimize to sell as much as possible, not to get you the best experience.
It's like asking for the most shopped articles that are the ones farther away. Is it difficult to design better supermarkets? Or are they just optimizing for you to spend more time and money inside?
If they had the full catalogue of all movies and series ever made then it'd easily be much easier to actually make more relevant recommendations, but their catalogue is actually shrinking as they have less old content they've been able to renew since those content owners have been starting their own streaming services.
Amazon, the book store has everything published under the sun and still cannot recommend something better than "oh, here you go, this is sci-fi as well!".
Soundcloud has amazing recommendations, which is the best feature of the platform in my view. It's so easy to find great music that's related to tracks you already like. I have found literally thousands of new tracks from its 'Station' feature.