Upside Down has a intriguing concept where there are two worlds, each with their own gravity, such that you can see the city in the sky. Unfortunately, the explanation of this phenomenon is weak. We are told that this is because two planets each have their own gravity (which is true), but this is not how it works in real life... also considering the fact that they are close enough for you to visualize in the sky and have skyscrapers joining the two together, this is disappointing. The other weak points are the "rules" of how this works, the major ones being that objects from their own world abide their own gravity, and that when matter between the two worlds are joined, they will eventually burn. Throughout the whole film, this is up to the plot's interpretation on whether to delay the effect or outright ignore it. It doesn't help that when you think about it, if one person is on the other side, the blood rushing to their head would probably kill them or at the very least, their hair should be standing on its end from the effects of the other's gravity. Ignoring all this, Upside Down is a love drama and it suffers from being a little bit dragged out and a rushed ending. We're given an evil organisation to hate and positioned to cheer on the main couple but their romance feels boring and underdeveloped. In the end, while it's far from a mess, there are quite a fair few plot holes and unnecessary convolution.