It totally deserved the top prize in 1940, it had great acting, no language at all...movies nowadays don't add up to this. Plus the plot was fantastic and the ending was totally unexpected.
Absolutely LOVE this movie, as well as the book by Daphne Du Maurier-- an absolutely wonderful love story that involves tragic mystery, and a main character's intense insecurity.
Hitchcock won his only Oscar for this film, and it was very well-deserved. I certainly recommend it (and the book) for both teens and adults.