I'm not an Englishman bro, so it's likely for me to make mistakes.
AFAIK, 'The last movie you've seen' is more acceptable because there's no emphasize on the time WHEN you saw the movie.
Just my two cents...
AFAIK, past tense is used when people want to emphasize when something was done, that's why often adverb is used to specify the time.
However, past perfect tense is used to emphasize that something has been done. When it was done, it's out of interest. That's why we never put adverb in past perfect tense.
AFAIK, the word "last" as used in "last movie" acts as an adverb.
Thus, IMO, it's more natural to say "Review the last movie you saw" instead of "Review the last movie you've seen".
Again, just my two cents too...