So they decided to keep some of the anti-semitism in without making it so obvious.
While there are some small but significant liberties taken, IMHO, they actually serve to better relate the larger themes and emphasize the more obvious symbols and back story.
As mentioned above, the device of Carraway writing from an institution sounds very contrived in speaking or writing about it, yet on screen - it worked. Similarly, the flashbacks to Gatsby's childhood, Dan Cody and his days as a junior officer were brief but very effectively contributed to the overall telling of the story.
In the movie, I heard the word "kike" used to refer to Jews, something I didn't see in the book.