I've been reading some late-'70s Superman comics recently, and it's amazing to see how much they were willing to shake up the status quo. It also makes me sad that the fanboys-turned-writers who grew up on the comics of this era (Meltzer, Johns, etc.) just want to return to those eras without restoring the attitude of change that made them interesting and memorable to begin with. Fodder for a future post, I guess.
1. Technically, it's not Clark, but Don-El, leader of the Kandorian Superman Emergency Squad, who deluded himself into thinking he was Superman, so Clark let him live his life for a day to shock him out of it. From "Superman (vol. 1)" #337.