Specifically. for letting Lincoln go on and on unnecessarily:
"I don't understand why it didn't just end when Lincoln is walking down the hall and the butler gives him his hat," he said. "Why did I need to see him dying on the bed? I have no idea what Spielberg was trying to do."
"I didn't need the assassination at all. Unless he's going to show Lincoln getting his brains blown out. And even then, why am I watching it? The movie had a better ending 10 minutes before."
To which Ebert heartily agreed on Twitter. Fascinatingly, the writer of the original, much-quoted story in the Los Angeles Times, Steven Zeitchik, actually managed to ask Spielberg about the ending (along with other directers, such as Tom Hopper, about their difficulty finding endings).
Speilberg defended his approach:
Asked about the prevailing feeling that he should have wrapped "Lincoln" at an earlier moment, [Spielberg] didn't concede the point. In fact, he said he didn't struggle with the ending as much as he did other issues. "The great challenge was not how the story would end but what it would cover," he said. "Tony [Kushner's] original draft was 550 pages."
As for Jackson's wish to see the shooter, Spielberg had an explanation. "We just knew we wouldn't show the assassination, because it would sensationalize the story. It would have suddenly focused the movie on the shooter, not the president."
To Jackson's question, Spielberg replies: I was only following the writer. And truly, that's what makes this movie unique among his many successes. It's a purely dramatic work, in which Spielberg stepped back, and put away his bag of tricks, and let the script and the actors provide the fireworks.
What a gift Lincoln was to us, then and now.