Indiana Jones and the Last Crusade (USA, 1989)
Directed by Steven Spielberg
Starring Harrison Ford, Sean Connery, Denholm Elliott, Alison Doody
IMDb Top 250: #98 (16/3/13)
Film franchises are subject to the law of diminishing returns. If a sequel is sub-par compared to the original, it's very unlikely that any third instalment could redress the balance, let alone be the best film in the series. Even if a sequel turns out to be good, or even slightly better than the original, the third instalment of a trilogy is so often the weakest film - Army of Darkness and Mad Max 3 being very good examples.
Holy Grail. It's still ultimately very silly - the Holy Grail has about as much to do with Christianity as flaming sacrifices have to do with Hinduism. But as with Raiders, the mythology is watertight enough so that the themes surrounding the Grail come out while working as a plot device. You can still view the Grail and the diary as McGuffins if you want to, but the film is more intelligent than Raiders in its connection of plot and theme, always inviting you to read more in without demanding it at the expense of the action.
The Empire Strikes Back, is a perfect fit for Walter Donovan, with the suave, well-dressed and well-spoken exterior disguising a dark, ruthless heart. And Alison Doody is very good as Elsa Schneider; while her character isn't as resourceful as Marian Ravenwood, she makes Elsa appealingly conflicted; we know what side she's on, and yet we keep asking questions about where her loyalty truly lies.