While there are some good freebies, they often are clunky and poorly integrated. I reckon that if you download 100, you might get a handful that are useful. I'm a firm believer in listening to the manufacturers stuff, and some are quite cheap - and then YouTubing to see what people think and listen to their efforts.
My expensive sample packages which I do keep buying are hugely better in every way. However Spitfire audio, who do expensive packages also have some really good totally free ones - in their Labs series. Google those. They just take little bits of the big packages and use them as loss leaders.