Agreed in general that 10 and even 5 is too much, and that 4 is a good compromise. Though personally I prefer thumbs up and thumbs down, plus a separate starring option. The first two signify “would I recommend this to anyone else” while the latter means “this has something interesting I’d like to revisit at a later date”. Something losing its star rating is par for the course, but the recommendation status is less likely to change (though it can happen). And yes, it is possible to give something a thumbs down and favourite it, e.g. when you don’t think something is particularly good or competent but it still had something which you recognise as meaningful to yourself specifically.

I don’t think this system is right for everyone, but I like it. Depending on the platform I may even use a rating system of 1, which represents the starring and everything else is just read/watched.