Hi Alexis, I have to say that I completely disagree with your teacher, and that your sentence is perfect! Well done!! It is strong, yes, but from the voice of a passionate person who is trying to be persuasive, it is a very common and perfectly well formed phrase. Where is your teacher from? She probably wants you to substitute "must" with "should", by the way. However, for me, in persuasive speaking, "should" is too weak. I hope this helps. Tom

In your sentence, "must" means that you strongly recommend others to watch the films. So your sentence is just fine. "Must" would be too strong in sentences like "You must apologize" (meaning that you have no other choice but to apologize), but in your sentence, it just reflects your personal opinion.

Take it from us - 'must' is fine here. It sounds perfectly natural to say 'you must watch' if you are being enthusiastic about the movie and want to encourage your friends to see it. And I agree that it sounds like this teacher of yours is in the wrong job!