Ziggy Stardust said:

I never really cared for Last Crusade. Maybe because it was too much like Raiders.

That's probably my reason too. I think it is a better movie than Doom, but at least Doom was visually different, and interesting. So I think Doom was a worthy sequel.

Crystal Skull pissed me off for how ugly the film was. The original Indy films had a beauty to them. Gotta tip your hat to Douglas Slocombe's keen eye. Plus any scene that could've looked good had a thick coat of yellow over it.

Lucas seems to have problems with 3rd films.