The word 微妙 originally means 'subtle', but it has recently come to be often used to mean 'not very good'. This usage is rather new, so younger people tend to use that way. I cannot tell the exact meaning of the sentence you show, but It appears to mean that movies are (or the movie is) not very good in some way.

Japanese people sometimes use roundabout or fuzzy expressions especially when talking about their negative opinion. There are straightforward Japanese though. Someone asked you, what did you think about something/someone else? But you didn't want to say anything negative directly, then you could say ビミョウー here. I don't know what about the movie was 微妙 by your context but something about it was not very good. In my opinion.