Taking ratings data from Rotten Tomatoes, Slate made a neat little toy called the Hollywood Career-O-Matic that tracks the movie ratings of actors and directors since 1985.
Most Improved: Josh Brolin, Dakota Fanning, and Ken Loach. If the average Hollywood career is a slow decline into mediocrity, an actor or director whose films actually improve deserves special recognition. Among actors with at least 20 films in the Rotten Tomatoes database since 1985, Brolin has seen the greatest increase in average rating from the first half of his career to the second half — an improvement of 28.4 percentage points. Despite Brolin’s early appearance in The Goonies (63 percent), the first half of his career was marred by abominations like The Mod Squad (4 percent), and Hollow Man (27 percent). His later transition into gems like No Country for Old Men (95 percent), Milk (94 percent), and True Grit (96 percent) is a tale of redemption that not even Wall Street: Money Never Sleeps (54 percent) could derail. The most improved actress is Fanning, with a 20.1-point increase from such duds as I Am Sam (34 percent) to critical darlings like Coraline (89 percent). Among directors, the award goes to Ken Loach, the British filmmaker whose reviews went from great in the first half of his career (80 percent) to stunning in the second half (88.1 percent).
For actors it would be interesting to see a similar analysis of box office gross and especially a weighted analysis that takes both critical acclaim and box office gross into account…the RT ratings for many actors are all over the place as they bounce from crappy big gross/paycheck blockbusters to lower grossing/paying critical darlings.