I think the most important thing the film can get right is the character of Jack. This film is supposed to start a franchise; really, Jack is of central importance. The rest, it really is just window dressing. People who know the source material are of course going to be far more concerned with the details, but the details are the least important thing when talking movie adaptation intended for a large audience.
I can't tell you how many people I know went to see the LotR films three or more times in the theater without understanding one single thing about the storyline. Why? Because the movies got the one thing right that was most important to the books--it got Middle Earth right.
Same applies here, with Jack. Make sure he's done right, and people will be drawn to the film, regardless of whether the baddies are Indian, Chinese, or from Mars.