Scary images for younger kids
Lots of the reviews on this site have been about the foul language. And to be clear, that is certainly present, and for families for whom this is important, be cautious. I wasn't bothered by the profanity - it came as comic relief in an otherwise fairly dark movie.
For us, what was most problematic was the violence. The villain (a Steve Jobs like character in charge of the robot factory) is actually a robot who has killed the human, assumed his identity, and is now trying to kill all the humans in the world. The "cartoon" violence that common sense lists in the description of the movie is actually quite explicit for an animated movie. Towards the end, when you begin to realize that the villain is a machine, his eyeball pops out and when he stands up, you see a red light coming out of the the empty socket. Very Terminator. That sequence was really disturbing for my kids. Also, in the climactic scene, the villain keeps coming back to try and kill the heroes, and each time, he looks worse and worse...more and more scary.
There are strong themes of friendship, memory, family, and loss...but the violence made the movie too scary for our kids (ages 10, 9, and 7).