In a recent Answer Man column, someone wrote in that a movie poster contained the blurb "Sure to be one of the best films of the year" and questioned the logic of praising a movie that the critic hadn't seen.
I think the "sure to be" part doesn't imply that the person hasn't seen the film, but they're reasonably certain that it will be one of the BEST films of the year.
It's a briefer way of saying "I have seen this film, but I have not seen every other film that will be released this year, so while this film is at this time among the best films that I have seen this year, I will have to reserve final judgment until such time as every film that will be released this year had been released, but in my past experience as a critic I know that there are few great films released in a single year, and so this one is quite likely one of the best of this year."
Since that won't fit on a movie poster, the original quotation should suffice.