Trying to complete his mission and atone for his mistake he spearheads the endeavours to help them get home but becomes marooned himself in the process.
I came to this having not even seen a trailer so knew nothing about how it fits in to the Toy Story franchise and surprise, in a very meta way it doesn't. They sidestep any weirdness by making this be the movie the toy is based on and then make a 100% standalone movie, which frankly is about the best way to handle it I can imagine.
They attempt to do an "Up" in the early section by having Lightyear watch everybody and everything he knows age, change and become irrelevant or die making him a fish out of water (who still thinks he's top dog) for the bulk of the film. This mostly works and even as it gets into the conventional action still plays with how the world changes and eventually leaves us behind.
Don't think this is philosophical stuff though it's a high action slapstick family movie. Some of the jokes are a bit repetitive but it rattles along nicely and the animation is excellent as you'd expect.
Not an amazing addition to the Pixar repertoire, it feels a bit throwaway, it does however entertain well while underway even if you'll never watch it again. 7/10 decently diverting especially given how sombre everything else is right now. Yes we know the Queen died but the festival of over earnest mourning in the UK media right now is excessive.