My favorite of the trilogy - Spoilers.

Rating: 9/10 (14 December 1999)

This is the best and most underrated of the trilogy, hands down.
My perspective may be a little skewed, because I actually saw the Indiana Jones movies in reverse order--"Last Crusade" was the first one I saw. I think that put me in a better position to appreciate it than the '80s-jaded critics and "Raiders" fans who wrote off the third installment as an inferior imitation.
I loved it. Even after seeing "Raiders" (which I liked) and "Temple of Doom" (which I hated), the third still ranks the best in my book. And why? Two reasons, which are intertwined:
It's FUNNY--much more comic relief than either of the other two, which keeps the tone light and the pace brisk. (One exception: the scene when Donovan ends up bargaining with his Rolls Royce--lame & totally extraneous.) I actually thought that "Raiders," not "Crusade," dragged in parts--I know it's heresy to say so-- because it seemed like a never-ending chain of rather heavy tho' suspenseful action sequences, without any of the laughs that livened "Crusade." I still laugh out loud every time I watch number 3.
Secondly it's funny mostly because of Sean Connery- a stroke of casting genius. He brings flair to the whole production, yet he doesn't hog the stage--he brings out the very best in Harrison Ford. Those two have such a hilarious, wonderful rapport; just notice the -looks- they exchange on the motorcycle ride, every time Indy plows down another baddie. Priceless.
The relationship btw. "Last Crusade" and "Raiders" is in some ways similar to that btw. "Return of the Jedi" and "Star Wars." In both trilogies, the third installment recycles a lot of the material of the first, but tries to flesh out the characters and deepen our emotional connection to them. The difference? "Last Crusade" is a -way_-better movie than "Jedi," and actually packs a surprising emotional heft in the last few scenes: I LOVE the moment when Dad (Connery) is reaching out to Indy and says for the first time, very quietly but oh so effectively, "Indiana." The Christian mysticism may feel slapped-on to some, but I actually liked it. And I'm an agnostic.
All in all, "Last Crusade" didn't feel at all stale or mechanical to me. It felt like fresh, glorious entertainment--a total joy-ride with surprising depths, owing largely to Connery & Ford--and still feels fresh every time I go back to watch it.