Kingdom Come was just a superman story with a bunch of cool character designs. A story that been done a thousand times before.
Earth X was more of a twisted celebration of the Marvel Universe and all it's weirdness. You had Tony Stark turning into Howard Hughes, a broken Captain America bumming around a former America trying to figure out what to do next. Cyclops fighting for mutant rights in a world full of mutants. And the twist at the end was so crazy, it still shocks me too this day.
Plus Mutant Hawkeye is the shit, dead during the story, but still hilariously awesome