SPOILERS...
For those of you who couldn't suspend your disbelief for certain scenes or the plot macguffin, consider the first three films and what they establish as "reality" within the Indiana Jones universe:
Temple of Doom: Hinduism is real.
Raiders: Judaism is real.
Last Crusade: Christianity (and possibly Islam, by extension) is real.
To add "extradimensional aliens are real" to that list isn't much of a stretch, isn't it? And once you've done that, you can pretty much forgive every scene where Indy should have broken his tail bone, drowned, gotten electrocuted, etc.
(Especially if you consider that there could be "higher powers" looking out for him.)