I don't think they made a good Indiana Jones movie after the original. Sacred rocks? Are you frigging kidding me? Stupid and ridiculous. The "Holy Grail"? Better, but they flubbed the plot. Crystal Skull was just silly and had no redeeming characteristics.
They should have done one about Excalibur or some such.
It was just like Star Wars. The original was a Gem, and sequels were dreck.
The Holy Grail was a pretty good movie and hit on a number of cylinders. I agree on Temple of Doom and Crystal Skulls, could have been much better.
The positive legacy of George Lucas will be all of the great special effects pioneered through Industrial Light and Magic. The positive legacy of Spielberg is in his many other terrific films, e.g., Jaws, Close Encounters, Schindler's List,etc.