If anyone is still looking to add Crisis on Infinite Earths to their digital catalog, all 12 issues are currently 99 cents apiece on Comixology, as are all the issues of Zero Hour: A Crisis In Time, Infinite Crisis, and Final Crisis!
Crisis (the idea for it) makes no sense. Per Marv Wolfman's fore/afterward, it was supposed to fix continuity issues. You don't fix continuity by adding on to the end of a storyline. The fact that people get killed or "worlds" get destroyed doesn't mean they didn't happen in the past. Also, Wolfman gives an example of continuity issues as Superman supposedly being the last Kryptonian, but later stories have all sorts of Kryptonians. This is not a continuity issue, it is a plot development. There are a near "Infinite" number of examples in fiction and real life where, what was once believed to be fact is found to be false. More Kryptonians makes more sense than one Kryptonian. Superman's father is the earth equivalent of a guy working on a spaceship in his garage. We are supposed to believe that a planet where technology is such that one guy can build a ship in his garage to keep an infant alive, while it travels across the universe unmanned and hit its target, doesn't have lots of people off-planet at the time Kryton explodes? That's a bigger stretch than only Superman survived.
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