Too many characters, narrators, quotable lines, and just anything else.
The film is about war in general, in that sense, it contains many washed out characters that seem just the same, not even one of them is memorable, this was one of the biggest fails of the film, the emotional connections. We don't know where most of the characters came from, what are their goals, why are they here.
The narration usually adds to the film, in this case, well, it doesn't. It's filled with "quotable" lines that are just useless, it got boring real quick.
The first and third act were intensely boring, second act was a bit good.
The movie is totally mediocre, meaning it should have a five star rating, why did I give it six? The cinematography. It was just beautiful and well executed, great production design and colors, great special effects.
Review of The Thin Red Line
