You can probably count on one hand the number of times the third film in a franchise wasn't the worst of the trilogy.
Weak third films: Return of the Jedi, Dark Knight Rises, X-men: The Last Stand, Spiderman 3, Hobbit: Battle of the Five Armies, Matrix Revolutions, Shrek the Third, Mummy: Tomb of the Dragon Emperor, Red Dragon (third Hannibal Lecter film), Terminator 3: Rise of the Machines, Alien 3, Austin Powers: Goldmember, Hangover III, Godfather III, Die Hard With a Vengence, Mad MAx: Beyond Thunderdome, Back to the Future III.
Then again, Goblet of Fire was very good, top third of all the HP movies. Return of the King was fabulous. MI:III was strong. Revenge of the Sith was the best of the awful prequels. Indiana Jones and the Last Crusade was better than Temple of Doom. Toy Story 3 may have been the worst of those three films but it was a truly amazing film.
-Jason "ok, that was a waste of my brain power
" Evans