I don't think I fully understand what they were trying to do with this.
I don't agree with those who are saying that this was just a marketing operation: if that was the only goal they could have easily made a much simpler, funnier movie. But this is a strange movie, and surprisingly bleak. They don't show you Buzz's status quo, his normal life on earth, and this is a bit destabilizing for the audience. The story starts with a failure and the characters get stuck with the consequences of that failure, and so the setting of the movie is a hostile desolate planet lost in the cold deep space. It's almost depressing. I mean, Interstellar, which is not a children's movie, is way warmer and more hopeful compared to this.
The movie it's still good, the story it's clever and the character arc is beautiful but it remains a bit emotionally empty. Sure, at the end he learns to appreciate the value of relationships, but he barely has any: he apparently doesn't have a family or a lover or someone waiting for him on earth, his only friend dies at the beginning and in a very upsetting way, in a montage that's like the disturbing version of the famous one from Up. Yes, he kinda bonds with that band of misfits, but they are not very memorable and they don't seem to build a deep connection with him. His most important emotional contact is with a robot cat, apparently.
Pixar is famous for strange, bold narrative choices, like making children's movies about old people and garbage robot, but here they seem to have gone too far. What turns out in the end is a movie that does not justify these choices with a clear authorial vision and is not even extremely commercial, and while their previous works were for both children and adults this runs the risk of not satisfying either of the two categories. Apparently, Pixar doesn't make you cry anymore. Now it just makes you sad.