I think the problem is if one movie sets a tone, we expect the whole franchise to follow that tone. It's certainly not a great film, but KOTCS is light and different, and I really don't mind that. Above all else, my main complaint was Mac, whom we hardly got to know before he betrayed Indy, and therefore it carried absolutely no emotional weight when he did. If I can buy the Ark frying a bunch of Nazis, an evil priest ripping out hearts and the victim surviving, or a cup aging someone hundreds of years in an instant, I can overlook the survival of a nuclear blast in a fridge. It's all fantasy anyway.