1. It's The Feature Length Version Of Jessie's Song - Toy Story 3
Toy Story 3 comes with the same visual polish you'd expect from Pixar, but some real unoriginality in the story department lets it down; ignore the nostalgia factor and it doesn't work anywhere near as well as the other entries in the series. Taking place about a decade after the original two films, the trilogy ender sees a grown up Andy about to leave home for college, forcing the toys to have to deal with their obsolescence.
It's a natural final act to a story that's already looked at other toy tropes like favourites and collectors, but doesn't really work because every major element in its execution is a retread of a key subplot to Toy Story 2. Jessie's Song is one of the best moments in the entire franchise, showing the effect growing up has on toys (and, depending on your reading of the series, parents); in four minutes we see Jessie go from being adored, to forgotten and eventually discarded. And in those minutes all the same emotion of Andy growing up is doled out without any contrived trips to the dumb.
Worst of all, the ending of Toy Story 3 uses the exact same resolution to the Jessie-Emily story; the toys find a way to buy themselves a few years of playtime and assume everything will be OK forever. As a definitive ending to the series it's a rather open-ended and unfulfilling final beat.
What other films took the easy route and heavily used another film for inspiration? Head down the comments and let us know your choices.