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This type of poster design, which uses several strips, each generally containing one of the film’s actors, is quite common. For example, this recent poster for Feast of Love uses it too.
Of course, within the constraints of this type of design there is still space for a lot of differentiation. Feast of Love is a light and romantic movie, so you get bright colors and a bunch of people smiling. Reservation Road is a much heavier drama, involving traffic accidents, deaths and a lot of soul searching. So you get darker colors and serious expressions.
There is a reason for the popularity of this type of design. It often makes for good looking and fairly effective posters, and it can be a good way to showcase all the actors in movies that are ensemble pieces. But it’s also a very safe approach that is unlikely to result in a truly great and memorable poster.