As someone who learned English purely from Hollywood movies, I can confirm its a solid way to learn a language. I even picked up the accent to the extent that I'm frequently asked if I'm American - even though I never lived in an English-speaking country.

It may not be for everyone though. The only reason why it worked for me is because I've seen so many US movies and TV shows. I started with subtitles and gradually moved to watching without them (though I had lots of difficulties understanding everything, especially in the beginning). I'd argue its a great way to learn the little language 'quirks', expressions, idioms, etc.