Raiders of the Lost Ark and Indiana Jones and the Last Crusade are two stand-alone films, but with the same main character.
Just like The Godfather and The Godfather Part II are two stand-alone films with two entirely different purposes.
Indiana Jones and the Temple of Doom has its moments at the beginning and the ending, but the midsection bogs the whole thing down.
Star Wars, The Empire Strikes Back, and Return of the Jedi make up the Star Wars films. Nothing else after 1983.