Despite receiving praise for its special effects,the movie was critized because its characters were so weak as 【being——to be】 scarcely belivable.
句意：
尽管因其特效而受到赞扬,但是这部电影却受到批评,因为它的角色/人物是如此的虚弱以至于几乎不可信.
按照句意表达,because从句中要表达【如此.以至于.】,对应的英语结构形式应该是【so/such...that/as to be...】,这里后面没有再用从句,而用了非谓语动词,所以,【being】应该改为【to be】.
祝你开心如意!