They both messed up things that have been very good in the past.
343i ruined a whole franchise, taking out core gameplay features that players have been accustomed to.
Microsoft took everyone's excitement for a new console and dumped it down the drain by making it more of an entertainment system than a video game console.
Although both are major disappointments, which one is worst?
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So both are hated by extremist fanboys who will take the tiniest details and will extrapolate it to be the mark of the apocalaypse. But when looking back with hindsight after doing research without being blinded by nostalgia/hate are both actually good-even if they defer from how they used to be.