I think the overriding theme of the Indy series is "You gotta have faith." In the end of each one, Indy overcomes his disbelief and rolls with the mystical events happening. Greed is bad cuz the bad guys keep trying to seize the artifact for themselves and usually (literally!) burn in the process, faith is good. The 3 sequels (okay 2 sequels and 1 prequel) also have a strong family theme. Does Raiders have a family theme? Lil bit, Indy is looking for Abner Ravenwood but ends up with his daughter / a girlfriend / "Your %#damn partner!!" Maybe not as much as the other ones but it's there.