I enjoyed halo 4 almost as much as halo 3, I figure there's no where better to go for a good answer than here.
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The story mode was good IMO, but it didn't capture the magic that the first three did for me. Also a horrible population and a restricted and confusing "custom" games at launch are to blame. I mean really, when people are modding the game with third party tools to implement something so simple such as no sprint, that's a problem.